One of the most extraordinary cases in which my old friend, Sherlock Holmes, was involved and with which it was my privilege to be associated began with a dramatic abruptness one hot Friday evening in August, some time after my marriage to Miss Mary Morstan.

Having not seen Holmes for several weeks, I had called on him at my old lodgings in Baker Street to find him in a wry mood, inveighing with mock exasperation against the dearth of interesting stories in the newspapers.

‘What has happened to all the criminals, Watson?’ he complained in a half-serious, half-humorous fashion. ‘Has the warm weather driven them all out of London to seek refuge at the seaside for the season? Not even the Daily Telegraph this morning could produce a single noteworthy case. It contained nothing but reports of regattas and garden parties. If this continues, I shall be forced to retire to the country and keep bees.’*

Hardly were the words out of his mouth than we heard through the open window the sound of wheels rapidly approaching and then drawing to a sudden halt outside, footsteps hurrying across the pavement and, seconds later, an agitated ringing at the front-door bell.

Holmes, who had been lounging back in his chair, sat up, instantly alert.

‘A woman judging by the footsteps,’ said he, ‘and in considerable distress, too. I believe, my dear old friend, that we are about to receive a new client and that my beekeeping will have to be postponed.’

At that, the door flew open and the woman in question rushed into the room.

It was a dramatic entrance, worthy of Grand Guignol or one of Verdi’s masterpieces for she had about her a dramatic, not to say operatic, intensity. Young, beautiful, with her black hair tumbling loose and wearing a light cloak which even my unprofessional eye could detect had been hastily thrown over her shoulders, she confronted Holmes, who had scrambled to his feet, with this impassioned entreaty: ‘Come at once! Is Isadora! ’E say, “Fetch Mr ’Olmes!”’

The message, spoken in a strong foreign accent, meant nothing to me but Holmes responded immediately. Seizing his hat and gesturing to me to accompany him, he ran after her down the stairs and out into the street where the four-wheeler in which she had arrived was still waiting.

There was only time, as the young woman was giving the driver an address in Kensington, for him to murmur to me, ‘The man is Isadora Persano, a well-known, international journalist and an old acquaintance of mine.’

Once the cab had started off, Holmes was able to question her and it was possible to piece together some account of what had happened; no easy task because of her broken English and the hysterical and barely coherent manner in which she expressed herself.

It seemed that Isadora Persano had retired to his study earlier that evening to write an article. At some point during the evening, quite when it was not clear, a small parcel, addressed to Persano, had been delivered to the house and had been taken upstairs by Juan Alberdi, a Mexican manservant.

Some little while later, she, Persano’s wife – although her hesitant manner in using the term suggested that their relationship had not been legalised – had heard Persano cry out and, on going up to the study, had found him, in her own words, ‘very, very bad, Mr ’Olmes’.

‘“Bad”?’ Holmes inquired. ‘You mean ill?’

‘Bad in ’is ’ead. Demente. Crazy. He look at this box in ’is ’and. Inside is a little creature; small; like a snake. But is not a snake. I do not know the English. It live in the ground.’

‘A worm?’

Holmes sounded quite incredulous.

‘Yes, yes; a worm!’ she cried, seizing eagerly on the word. ‘A little worm. Isadora crazy when he looks at it.’

However, it appeared that Persano had managed to recover his sanity for a few moments, long enough to gasp out the one word ‘Holmes!’, an exclamation which she had perfectly understood as Persano had previously warned her that, should anything happen to him, she was without delay to contact Mr Sherlock Holmes, Persano’s old friend the consulting detective, at 221B Baker Street.

Holmes was about to ask her why Persano had thought it necessary to give her these instructions when the cab drew up outside a tall house in a quiet Kensington side-street and Señora Persano leapt out and was running up the steps to the front door which was set wide open.

Holmes and I hastened after her, Holmes pausing only to fling some coins at the cab-driver.

Inside the house, I had a fleeting impression of a small, dark-faced man, presumably the Mexican manservant, cowering in a state of great terror at the back of the hall, before I followed Holmes and the Señora up three flights of stairs to a landing at the very top of the house where she unlocked a door and threw it open.

The scene which met my eyes almost defies description.

It was a study, lined with bookshelves and with a desk, on which was burning a single green-shaded lamp, placed at right angles to an open sash window which overlooked the back of the house.

A man was seated at the desk, crouched over and gazing down with great intensity at a small box which was lying in front of him. He was tall and well-built, with a deeply sunburnt face of a strong, hawklike cast, marked with a scar on his left cheek, and would have been handsome apart from the expression of mad frenzy which convulsed his features, setting his eyes rolling in his head and clenching his lips open in a terrifying grimace.

In the green light from the desk-lamp, he had the appearance of a tortured soul from a medieval illustration of the inferno.

Hardly had I time to absorb these details when, with a dreadful cry, the man jumped to his feet, overturning the chair as he did so and sweeping the papers off the desk with one wild lunge of his arm.

As they fluttered to the floor, he flung himself at the open window and, while we stood, horrified and transfixed in the doorway, disappeared from sight over the edge of the sill with another ghastly scream, as if all the demons of hell were at his heels.

There was a moment of absolute silence before the room erupted.

With a wild cry of her own, Señora Persano rushed to the window and would have hurled herself after him had not Holmes seized her by the waist and, spinning her round, slammed the sash down. The next moment he had bundled her out of the room on to the landing where he locked the door and pocketed the key before setting off down the stairs, I at his heels.

We raced through the house, past the cowering manservant in the hall and into a kitchen where a fat, red-faced cook and a thin, sharp-featured maidservant looked up from their tasks to gape at us, and from there through a door into the back garden where we found the body of Isadora Persano.

Despite my own experiences of violent death and appalling wounds in battle when I served in India as Assistant Surgeon during the second Afghan war, I hesitate even now in describing the scene.

Persano had fallen from the top storey on to the railings which surrounded the basement area with such force that two of the iron rods, tipped with spear-shaped spikes, had penetrated his chest to a depth of several inches.

Although I knew the task was hopeless, I felt for the carotid artery in his neck and, finding no pulse, I turned to Holmes.

‘I am so sorry; there is nothing I can do. I am afraid he is dead.’

Rarely have I seen my old friend in such a state of shock. In the light streaming out of the open kitchen door, his features looked bleached, his lids drawn so far down over his deep-set eyes that they appeared hooded, like those of some gaunt, brooding, melancholy bird. But even in this first moment of horrified awareness of the tragedy, he was still in command of his reactions with that icy self-control which has led me at times to accuse him of deficiency in human sympathy.* I fear I may have maligned him. It was not always lack of emotion on his part but a deep-seated dislike of revealing to others those feelings which lay closest to his heart.

Within seconds, he had recovered sufficiently to take charge of the situation.

With the curt comment, ‘We must send immediately for the police,’ he strode back into the kitchen where, tearing a page from his notebook, he hastily scribbled a message which he handed to the servant girl with orders to deliver it immediately to Inspector Lestrade at Scotland Yard.

The girl having departed with the note and the money for the cab fare, Holmes turned to the red-faced cook.

‘You speak English?’ he demanded.

‘That I do, surr,’ the woman replied in a strong Irish accent.

‘Then accompany Dr Watson upstairs and see what you can do to comfort your mistress.’

Indeed, we could hear even on ground level the young woman’s hysterical sobbing echoing down from the top of the house.

Between us, the cook and I supported Señora Persano into her bedroom on the second floor where I administered smelling-salts and brandy. Once she had grown a little calmer, I left her in the care of the cook, who seemed a sensible enough woman, and returned upstairs to the study to join Holmes, who had passed us on the landing.

On entering, I found that he had lit the gas jets over the fireplace and it was possible to see more of the room.

It was a low chamber with sloping attic ceilings and a small hearth in which was set a basket grate, empty because it was summer of anything except some crumpled sheets of paper, covered with handwriting which I assumed was Persano’s.

As I came in, Holmes, who was kneeling in front of this grate, carefully examining its contents, leaned forward with an exclamation of satisfaction and retrieved a square of coarse yellowish paper, quite different in colour and texture to the others.

‘What do you make of this, Watson?’ he inquired.

In my absence, he seemed to have recovered some of his usual control, apart from a certain grimness about the set of his mouth.

I said, ‘Judging by the creases in it, it has been folded up to form a kind of packet. In fact, it reminds me of the old-fashioned apothecaries’ method of wrapping up powders. Isn’t that a small blob of wax still adhering to it where the edges had been sealed?’

‘Correctly deduced, my dear fellow. The packet was indeed fastened with wax and then the seal was broken; fairly recently, too. The piece of paper was lying on top of the others in the grate but, while they were sprinkled with fine soot from the chimney, this was quite clean. However, you failed to remark that the paper is of a poor quality, foreign make and that some small grains of a brownish powder are still adhering to the folds; too few, though, I fear, for successful analysis. We shall see what Lestrade has to say about it,’ Holmes concluded, placing the square of paper in his pocketbook before conducting me across the room.

‘And the desk, Watson? What deductions can you draw from this?’

It was a large desk but apart from the evidence which suggested that Persano had been working at it shortly before he plunged to his death, demonstrated by the open book – in Spanish, I noticed – and the scattered papers lying on the floor, I saw nothing.

Except, of course, for the worm.

I stooped down to peer at it gingerly.

It lay curled up in a matchbox and was a most curious creature. About the size of an ordinary earthworm, it was quite unlike any other I had ever seen before.

Along the length of its back ran a line of tiny, black spots which spread out over the head to form a V-shaped pattern, similar to the markings on a viper.

It stirred and I hurriedly backed away.

‘What is it, Holmes?’ I asked. ‘Is it venomous? Was Persano bitten by it and this caused him to go mad?’

‘It would certainly appear so,’ Holmes replied. ‘It would also seem that the small parcel which was delivered to the door earlier this evening contained the matchbox inside which was placed the worm. You no doubt noticed on the desk the piece of brown paper in which the package was wrapped with Isadora Persano’s name and address written on it; not in an English hand, however. The writing has a foreign look about it.’

I could no longer contain my curiosity.

‘Who is Isadora Persano and where did you meet him?’

‘Persano was,’ Holmes corrected me quietly, his eyes again hooded over with their lids, ‘an internationally renowned journalist, who specialised in South American affairs. I met him several years ago under unusual circumstances in Paris where he was investigating the sale of forged Peruvian works of art for a newspaper article. Indeed, he claimed to have Inca blood in his veins. There was also a Spanish mother and a Quechua Indian grandfather. However, his antecedents are of little relevance to his death.

‘A few weeks ago, I received a letter from him, informing me that he had recently returned from Mexico where he had been for the past six months, researching for a particular assignment, of what exact nature he did not specify. He suggested we should meet but unfortunately at the time I was engaged with the case at Longwater concerning the stolen diamond necklace.

‘Once the investigation was completed, I had every intention of writing to him again to suggest a date for the proposed meeting. I fear I have left it too late.’

The last remark was spoken in a tone of deepest despondency.

‘Did he mention in his letter that his life was threatened?’

‘Not in so many words. He merely wrote that he had made many enemies while in Mexico but, as he was an expert duellist, both with sword and pistol, and was used to defending himself, I did not regard it as significant. He received that scar on his face during an attack by hostile Indians while on an earlier expedition to the Amazonian rain-forests. I very much regret that I failed to take his statement more seriously. He clearly considered himself in danger if he warned Señora Persano to contact me.’

To comfort him a little, I said, ‘The Señora will surely be able to tell you who his enemies are.’

‘Yes; indeed I must question her.’

‘But not tonight, Holmes,’ I urged. ‘She is in no fit state to be cross-examined.’

Holmes acquiesced reluctantly.

‘Very well, Watson. I am forced to bow to your professional judgement but at some point, and soon, she must be persuaded to tell us what she knows. And now, my dear fellow, before Lestrade arrives, take a final look at the desk and tell me if you have observed anything else which might be useful to the inquiry.’

I looked but could see nothing.

‘No, Holmes. Only book and papers.’

‘Well, well!’ said he in a tone of mild surprise but he would not explain what, if anything, I had failed to notice and, turning about, he crossed to the shelves to examine the titles of the books, a task which occupied him until the arrival of Inspector Lestrade, who was accompanied by several other police officers.

Lestrade listened in silence to Holmes’ account of what had happened from the time Señora Persano had arrived at Baker Street to Persano’s leap from the window but he seemed less interested in Holmes’ discovery of the piece of paper in the grate than in the matchbox containing the worm.

As I had done, he approached it cautiously, bending down to peer at it and taking care, I noticed, to keep his hands clasped behind his back.

‘Extraordinary!’ he exclaimed. ‘I have never seen anything like it before. A species of adder, would you say, Mr Holmes? It has the markings of one. I shall have to get this examined by an expert. But there is no doubt in my mind that it caused Mr Persano’s sudden madness. It must have bitten him when he opened the box. Nasty-looking little thing, isn’t it? It is going to need careful handling.’

Holmes said nothing during this monologue, merely standing by and watching as Lestrade sent one of his constables downstairs to ask the cook for a tin box with a well-fitting lid, a pair of thick leather gloves and some fire-tongs.

It was only after these articles had been produced and Lestrade, wearing the gloves, had picked up the matchbox with the tongs and deposited it very slowly and carefully inside the tin while an attendant subordinate clapped on the lid, that Holmes ventured a remark.

‘Well done, Inspector!’ he exclaimed.

Lestrade looked round, beaming with satisfaction. He had not apparently noticed the ironic tone in Holmes’ voice nor the amused gleam in his eyes.

‘And now that the little fellow’s shut away,’ he announced, ‘I can make a start on the investigation.’

‘You intend on speaking to the servants?’ Holmes inquired.

‘Not for the moment, except for the girl who took in the parcel,’ Lestrade replied with an offhand air. ‘I shan’t waste much time on the others. In my opinion, no one in the household is involved. We already have the villain who is responsible safely under lock and key.’

Laughing at his own joke, he rapped with his fingers on the lid of the tin.

‘You have no objection if I question them?’

‘Ask all you want, Mr Holmes. I shall be busy up here until the police surgeon arrives and I can arrange to have Mr Persano’s body removed to the mortuary.’

However, as Holmes and I went to the door, Lestrade clearly had second thoughts for he suddenly asked, his sallow features sharp with suspicion, ‘If any of them has anything useful to tell you, you will let me know, won’t you, Mr Holmes? With your permission, I shall call at Baker Street tomorrow evening to discuss the developments in the case.’

‘Of course, Inspector,’ Holmes said graciously.

There was no sign of the Mexican manservant when we went downstairs to the hall, only the cook and the servant-girl whom we found in the kitchen, discussing with a horrified but excited animation the events of the evening, with the back door to the garden where Persano’s body was still lying firmly closed and the blind drawn down over the window.

Holmes spoke first to the cook.

Once we had succeeded in comprehending her thick brogue, we learned little from her except for the fact that her name was Mrs O’Hara and that she did not live in but had been engaged as a cook-general on a daily basis from the time when Mr Persano had rented the house furnished two months earlier. She saw little of Mr Persano himself who spent most of the day upstairs in his study and rarely went out. The Señora, whom she referred to as Mrs Persano, was in charge of the household and gave the orders although how the two of them managed to communicate, the one with only a limited knowledge of English, the other with an almost impenetrable Irish accent, was a mystery in itself.

The servant-girl, Polly Atkins, was a quick, alert little Cockney. As she lived in, she was able to tell us a little more about the occupants of the house and Isadora Persano’s daily routine. She confirmed the cook’s statement that Persano rarely left the house and, in the short time he had lived there, had received no visitors and hardly any letters.

‘Except for a small parcel which I understand was delivered this evening,’ said Holmes. ‘Who took it in?’

‘I did, sir,’ she replied promptly. ‘It came about ’alf past seven, brought by a young lad.’

‘Can you describe him?’

‘Well, he was just an h’ordinary boy, sir. I didn’t take no particular notice. ’E said the parcel was h’urgent and ’ad to be ’anded to Mr Persano straight away.’

‘What did you do with it?’

‘I give it to Juan to take upstairs. I’d ’ad strict h’orders not to disturb Mr Persano while he was writin’ so, as me and Cook was busy in the kitchen, I reckoned Juan could do somethin’ to earn ’is keep. ‘E’s Mr Persano’s manservant; not that ’e does much except wait at table and clean the silver.’

‘Where would I find this Juan?’

‘In the boot-cupboard, under the stairs.’

‘The boot-cupboard?’

‘’E allus ’ides in there when ’e’s upset. But you won’t get nothin’ out of ’im,’ she added, as Holmes made for the door. ‘’E’s a proper ’eathen; don’t speak a word of h’English.’

This proved only too true when, having located the boot-cupboard and found Juan closeted inside it, Holmes hauled him out into the light of the hall.

He was a small, dark-skinned youth with the broad and slightly flattened features of an Indian peasant and might have been any age from twelve to twenty for he had the old-young look I had observed before in the faces of London street-urchins who have grown wise beyond their years in the ways of the world.

He exuded fear. We could smell it on him – that feral odour which a terror-struck wild animal gives off when it is captured, and he clutched wildly at a gold crucifix about his neck as Holmes dragged him forward by the sleeve.

But we could get no response from him except for a dumb shaking of his head, even when Holmes tried him with a few words in Spanish.

Eventually, realising the task was hopeless, Holmes released his grasp and the youth bolted up the stairs.

‘Let him go,’ Holmes said, as I prepared to start after him. ‘We shall have to question him again tomorrow in Señora Persano’s presence. She will be able to act as interpreter.’ He seemed suddenly weary for he passed a hand over his eyes before continuing, ‘There is nothing else we can do here for the time being. Let us find a cab and return to Baker Street.’

Outside in the street, we hailed a hansom and, as it drew up outside his door, Holmes said, ‘Keep the cab, Watson. I should prefer you not to come in with me. I am in no mood for company and besides there is some research I must undertake which will engage all my attention. But should you be free tomorrow afternoon at two o’clock, my dear fellow, I shall be delighted to see you.’

As he climbed out of the cab, he added in a musing tone, half to himself, ‘I wonder if Mrs Hudson has such a thing as a garden spade?’

Although I could understand his desire to be alone so soon after the death of his friend, I was nevertheless a little hurt by this dismissal and also intrigued by Holmes’ parting remark. What possible use could he have for a garden spade?

It was a question which absorbed me on the homeward journey and one which I was convinced I had answered by applying Holmes’ own deductive processes when, at two o’clock the following afternoon, I again presented myself at 221B Baker Street where I was admitted by Mrs Hudson.

‘Were you able to supply Mr Holmes with a spade?’ I asked, eager to put my theory to the test.

‘Indeed I was, Dr Watson, although goodness knows what he wanted it for. He was out with a lantern turning over my flower-borders until gone midnight.’

Although I thought I could guess what lay behind Holmes’ nocturnal activities, I was still not prepared for what he had to show me.

‘I hear you were out last night digging for bait,’ I remarked in a jocular fashion as I entered the sitting-room. ‘Were you successful?’

‘If by bait you mean the worm which was used to hook Persano,’ said he, ‘my efforts were rewarded. Come and look at this, Watson.’

Lying on the table was a saucer and in the saucer, stretched out at full length, was the remarkable worm which I had last seen curled up in the matchbox on Persano’s desk, marked with the same line of fine black dots along its back and the chevron pattern on its head.

‘Where on earth did you get it from, Holmes?’ I asked, assuming that he had acquired it from Lestrade by some nefarious means.

‘Not on earth, Watson,’ he corrected me with a smile. ‘In earth. It was one of several that I dug up last night from Mrs Hudson’s back garden.’

‘Several? I don’t understand. Is there a sudden plague of these creatures? If so, should we not inform the police or someone in authority? They are venomous, are they not?’

Holmes burst out laughing and, although I was a little annoyed to be the source of his amusement, I was nevertheless gratified that he had recovered his good spirits after his low state of mind the previous evening.

‘Take my word for it, my dear fellow, it is perfectly harmless!’

‘But the markings …’

‘Indian ink,’ Holmes explained and, taking me by the arm, led me over to the table where he conducted his scientific experiments and where I saw several more dishes laid out in a row, each containing a worm with similar markings although on all of these the lines of dots were not nearly so distinct.

‘My first attempts,’ Holmes continued. ‘I tried various substances as you can see from the bottles and jars: ordinary black ink, boot polish applied with the point of a pin – a singular failure, that particular one; the polish rubbed off too easily. Dye and paint were too liquid; so, too, was stove blacking. If you ever wish to draw a pattern on an earthworm, Watson, allow me to recommend Indian ink, applied with a fine-nibbed mapping-pen.’

‘So Persano wasn’t bitten by the worm?’

‘No; although that was what we were meant to believe,’ Holmes replied, his eyes once more assuming their sombre, brooding expression.

‘Then how was he sent mad if it wasn’t by some kind of poison?’

‘That is what I propose asking Señora Persano this afternoon. I also intend to discover what was in the glass which had been placed on Isadora Persano’s desk at some time yesterday evening.’

‘What glass, Holmes? I saw no glass.’

‘The object does not have to be present in order to convince one of its physical existence. It is not necessary for the bank manager to be confronted by the actual burglar for him to know his premises had been broken into. The blown safe is evidence enough. It was so in this case. Although the glass had been removed, it had left behind a ring which had marked the polished surface of the desk. As the stain was still damp, I deduced that the glass had been removed not long before our arrival and Isadora Persano’s death. As the cook had no reason to go up to the study and the servant-girl was positively ordered not to do so, the only persons who could have taken the glass upstairs and then removed it were either Juan Alberdi or Señora Persano. I propose to find out which of the two it was. Come, Watson. The Señora should have recovered sufficiently to offer some explanation, if not the whole truth.’

Señora Persano had indeed recovered to the extent that she was no longer confined to bed but was lying on a sofa in the drawing-room, to which Polly Atkins, the little maid-of-all-work, conducted us.

It was one of the strangest rooms I have ever entered. Although it was furnished with the conventional items that are usually supplied with a rented house in the way of armchairs, occasional tables and whatnots, every surface was covered with an extraordinary collection of South American objets d’art which Persano must have brought back with him from his travels. There were woven rugs, painted pottery, carved figurines, all brightly coloured, and, weirdest of all, a whole wall filled with masks of gods and goddesses, saints and demons, some grotesquely grinning, others grimacing in pain or terror.

It was not a room in which one could feel at ease, especially as the blinds were drawn against the bright afternoon sunshine, and I was surprised that Señora Persano had chosen such a setting in which to convalesce although no doubt these bizarre objects were familiar to her.

She lay in the semi-darkness, covered with a silk shawl which was embroidered with exotic birds and flowers, looking very pale and languid, her black hair loose about her shoulders.

We approached the sofa and, drawing out two upright chairs, sat down at her side, I taking care to place my own seat so that it had its back to the masks.

I still have my notes and from these, I have drawn up a summary of the conversation between Holmes and the Señora. It was conducted at times in Spanish, Holmes translating for my benefit, but largely in English, heavily fractured on the Señora’s part and frequently interrupted by tears, sighs and impassioned lamentations in her own language.

However, little by little we were able to put together her story.

She had met Isadora Persano in Argentina the previous year when he had been travelling through South and Central America gathering material for a book he proposed writing on the subcontinent as well as for a series of newspaper articles, commissioned by the Washington Gazette.

They had fallen in love and, when he moved on to Chile, Brazil, Ecuador and finally to Mexico, she had accompanied him.

There was no mention of a marriage ceremony and I noticed that Holmes was careful not to query this point.

In Mexico, Persano had been engaged in collecting information about the Porfiriato under the dictator, General Díaz.*

Later Holmes was to explain to me the meaning of the Porfiriato and its political implications. After General Díaz had seized power in 1876, the country had been developed economically but at the cost of great human suffering and loss of personal freedom, particularly among the Indian peasants whose communal fields had been confiscated to enlarge the private estates of the Spanish-speaking landowners, encouraged in their actions by the General’s policy of pan o palo, bread or the club.

It was this aspect of the General’s dictatorship which particularly interested Persano, the Señora informed us. With his own Indian ancestry and his wide knowledge of the South American indigenous culture, he had sympathised strongly with the sufferings of the landless peasants.

It was for this reason that he had taken Juan Alberdi into his employment, having found the boy starving on the streets of Monterrey.

In the course of his researches, Persano had made many enemies, chief among them Carlos Vicente Gasca, a rich and powerful landowner who was notorious for his ill-treatment of the Indian peasants who worked his estates.

Persano had threatened to expose Gasca in his articles for the Washington newspaper. Gasca, in turn, had vowed to kill Persano.

There had been several attempts on Persano’s life. He had been shot at twice while out riding. On another occasion, a man had broken into their hotel bedroom late one night and had attacked Persano with a knife. Persano had fought him off and the man had escaped.

After each failed attempt, Persano had received a piece of paper on which was drawn a skull, accompanied by a warning in Spanish that the attacks would continue. Persano was convinced that these had been sent by Gasca.

Realising that the next attempt might be successful, Persano had decided to return to England, bringing with him the Señora and Juan Alberdi. He thought that he would be safe in London, where he would have the time and leisure to write his book and his newspaper articles without being under the threat of imminent death.

But Gasca must have followed him and found out where he was living because two weeks before, Persano had received through the post a sheet of paper bearing the skull and the warning.

It was then that Persano had told the Señora that if anything happened to him, she was to contact his old friend, Mr Sherlock Holmes, and had given her Holmes’ address.

‘Why did he not come to me himself?’ Holmes exclaimed in some distress.

‘’E was too orgulloso; also tenaz,’ Señora Persano explained, which Holmes translated for my benefit as ‘proud’ and ‘stubborn’. ‘’E thought if ’e stay at ’ome and do ’is writing, there is no danger.’

She could give no detailed description of Gasca. Persano had been careful not to involve her in his political activities and she had seen the man only once, at a distance.

From her gestures, I gathered he was tall, ‘alto’, and broad-shouldered with dark hair, ‘muy ondulado’ – very wavy. He also spoke good English – ‘like a milord’.

As Holmes was to point out to me later, it made the task of tracking down Gasca extremely difficult. With a little disguise, such as a wig to cover his dark, wavy hair, he could easily pass himself off as an Englishman.

We then came to the events of the previous evening, painful both for Holmes and for Señora Persano, who frequently broke down in tears, but eventually, after much patient questioning on Holmes’ part, a coherent account emerged.

Immediately after dinner, Persano had retired to his study, his habit on a Friday evening. During the week, his time was spent on his own book but Saturdays and Sundays were always set aside for writing the articles for the Gazette, which had to be posted on Monday.

Señora Persano knew nothing about the arrival of the parcel until later. The servant-girl had accepted it from the messenger and Juan had taken it upstairs. She herself had remained in the drawing-room, reading.

At about nine o’clock, she had heard Persano cry out and had gone upstairs to find him in the demented state she had described to us the previous day. When he had shouted out the name ‘Holmes!’, she had run out of the house and had immediately taken a cab to the address in Baker Street which Persano had given her.

And that was all she could tell us.

‘I think not, Señora Persano,’ Holmes said quietly. ‘I believe you went upstairs to the study earlier in the evening to take Isadora a glass containing some kind of beverage in which you mixed a certain powder. I found the paper in which the powder had been wrapped in the grate. There was also a damp ring on the desk where a glass had stood. What was in that powder?’

Her response was immediate. Flinging herself back against the sofa cushions and covering her face with her hands, she burst into a flood of tears.

‘Nothing!’ she wept. ‘I swear it!’

Holmes rose to his feet, his expression stern and unforgiving.

‘In that case, Señora, you leave me no alternative. I shall be forced to place the facts before Inspector Lestrade.’ When she said nothing, he continued, his voice rising, ‘Do you not realise you risk being accused of causing Isadora’s death? I do not believe you were responsible. But unless you tell me the truth, there is nothing I can do to save you.’

She sobbed helplessly for several minutes while Holmes and I sat by watching, he impassively, I deeply moved by her distress and also seriously concerned about the state of her health.

At last, drawing a deep, shuddering breath, she spoke.

‘The powder is not ’armful. Is made from guarana seeds.* Is an old remedy, used by the Quaramis, to stop people from sleeping. Isadora buy in Brazil. ’E use it to keep ’im awake when ’e writes ’is stories for the newspaper. I give ’im in warm milk.’

‘When?’ Holmes demanded.

‘Every Friday evening. Then ’e work all night.’

‘And where do you keep the drug?’

‘In there.’

She gestured towards a small bureau which stood against the far wall. Holmes stalked over to it and, jerking open the drawer, revealed a small pile of folded packets, made from the same coarse paper which he had retrieved from the study grate.

Unwrapping one, he showed me its contents – a brownish powder, similar in colour and texture to that which had been adhering to the folds of the packet found upstairs.

Behind us, Señora Persano was protesting, ‘The one I give ’im Friday is one of those; is the same.’

His expression grim, Holmes refolded the paper square and put it away in his pocketbook, remarking to me in a low voice as he did so, ‘I doubt that very much. The drawer is unlocked. Anyone in the household could have opened it and replaced the top packet with another. I propose questioning Juan Alberdi now, Watson, with the Señora acting as interpreter.’

It was at this point that I intervened, disastrously as it later transpired. Had I not done so, a life might have been spared.

‘I cannot allow that, Holmes. Señora Persano is on the verge of a breakdown. As a medical man, I consider it most unwise to press her further. Come back tomorrow, if you wish, to interview the manservant. For the moment, however, I must insist that she is allowed to rest.’

Holmes acquiesced reluctantly and shortly afterwards we left, having made sure that Señora Persano was placed in the care of Mrs O’Hara.

As soon as we returned to Baker Street, Holmes went immediately to the bookcase and, pulling out volume ‘D’ in his encyclopedia of reference, opened it at a certain page and handed it to me silently.

I read:

Holmes meanwhile had flung himself down in his armchair where he sat, his chin propped on his long fingers as he stared moodily into space.

When I had finished reading the passage, he said abruptly, ‘You see the implications, Watson? Someone in the household was persuaded by Gasca to substitute for the packet of guarana seed powder which Persano took regularly every Friday evening as a stimulant another packet containing a hallucinatory drug made from the Psilocybe mushroom, which his system was unused to absorbing. All the symptoms were present in his apparent insanity – the ‘berserk’ state, the frenzied expression. Even his leap from the window can be attributed to the effects of the drug, which can induce in the person who takes it the belief that he can fly.’

‘And you think that the culprit was Juan Alberdi, the manservant?’

‘It is unlikely to be the other servants. How would they have access to such a drug? As for Señora Persano, she had nothing to gain and everything to lose by Persano’s death. She is now left alone in a strange country with no protector.’

‘But I do not see why Alberdi should have conspired with Gasca, Persano’s sworn enemy. After all, Holmes, Persano had saved the young man from starvation. Alberdi had every reason to be grateful to him.’

‘Not if the bribe Gasca offered were large enough. For some people, loyalty is like any other marketable commodity, to be bought and sold at the right price. Or Gasca may have threatened Alberdi in some way. It is also possible, of course, that Alberdi was persuaded that the drug he substituted was perfectly harmless. There is, however, no doubt in my mind that Alberdi was used as Gasca’s tool. You should have allowed me to question him this afternoon.’

‘Tomorrow will be soon enough, Holmes. In the meantime, Lestrade said he would call on you this evening. Why do you not speak to him and ask him to take Alberdi into custody for questioning? I am sure the Inspector could arrange to have a Spanish-speaking interpreter on hand when you interview the young man. That way, Señora Persano will not be placed under further stress.’

‘You are probably right, my dear fellow,’ Holmes agreed. ‘But such arrangements must be made as soon as possible. Gasca must be somewhere in London, no doubt staying at a hotel. I am eager to run him to earth before he has the chance to leave the country. For you may be sure that, once he hears of Persano’s death, he will not delay in making his escape.’

Lestrade arrived about an hour later, more eager to inform us of what he knew, or rather what he did not know, about the remarkable worm than to listen to Holmes.

‘Extraordinary!’ he exclaimed as soon as he set foot inside the room. ‘I have looked up that creature in every book on snakes and reptiles I can lay my hands on and nowhere is it mentioned. It would appear to be unknown to science. Where do you think it came from, Mr Holmes? Some South American jungle or Mexican swamp?’

‘I suggest you try a London park or garden.’

Lestrade stopped short, his mouth open in astonishment.

‘You are not serious?’

‘Indeed I am. Allow me to show you my own specimen, dug up from Mrs Hudson’s flower-border only yesterday.’ Holmes fetched the dish on which the earthworm was lying, adding as the Inspector backed away, ‘There is no need to be alarmed, Lestrade. The creature is perfectly harmless. I myself painted on the markings with Indian ink.’

It was highly gratifying to see Lestrade’s amazement and to hear him stammer, ‘I don’t understand. Why was the creature sent to Persano if it had nothing to do with his death?’

‘It was a cunning ruse to throw us off the scent. The villain behind the plot intended that the police should waste time following up this false clue, thus giving him the opportunity to leave the country.’

Holmes then gave Lestrade a brief summary of what he had learned that afternoon from Señora Persano and his suspicions regarding Gasca, concluding with the words, ‘You must put as many men as you can spare, Lestrade, on checking the hotels. It will not be an easy task, made more difficult by the fact that Gasca speaks good English and will no doubt be travelling on false papers. All that Señora Persano could tell us was that he is a tall, broad-shouldered man with dark, wavy hair, but that latter feature can be easily disguised. However, as he is rich and is used to having servants to wait on him, I suggest he will have at least one companion, possibly two. As for the boy who delivered the package containing the worm, take my advice and do not attempt to trace him. He is no doubt some urchin whom Gasca paid to run the errand and who will be impossible to identify from among the hundreds like him who roam the streets of our capital. In the meantime, we must return at once to Persano’s house and take Alberdi into custody for questioning. It was he, I believe, who was bribed or coerced in some way by Gasca to substitute one packet of drugs for another.’

But we were too late. By the time we reached the house, Juan Alberdi had already fled. The only information we could learn of his departure was from a very embarrassed police constable whom Lestrade had left on duty at the front door and who told us that the manservant had gone out earlier that afternoon, carrying a letter in his hand as if on the way to post it, and had not yet returned.

Lestrade was furious but there was nothing he could do. He had left no instructions that anyone should be prevented from leaving the premises.

‘God knows where he could have gone to,’ the Inspector said gloomily, turning to Holmes.

‘Can’t you guess, Lestrade? The young man was terrified of being accused of causing Persano’s death. I suggest he has gone to seek out Gasca. Find one and you will find the other.’

‘That is easier said than done, Mr Holmes,’ Lestrade replied.

However, he did the best he could under the circumstances, issuing a description of Alberdi together with orders that, if found, he was to be arrested. He also instituted inquiries for Gasca and the missing manservant at all the London hotels.

There was nothing Holmes and I could do to assist this part of the investigation and we returned to Baker Street, where my old friend immediately retired to his bedroom and sought what solace he could find in playing the violin.

I was much concerned about his state of mind. However much my old friend might try to disguise his feelings, he was still deeply affected by Persano’s death and blamed himself for not having contacted the man to suggest a meeting. He was convinced that had he done so, he might have learned of Gasca’s threats and helped to save Persano’s life.

I was afraid that, in his present mood, he might revert to the use of cocaine, a pernicious habit from which I was slowly managing to dissuade him.*

With this fear uppermost in my mind, I called several times at Baker Street over the next two weeks, anxious not only about Holmes’ condition but also about the progress of the case.

Nearly a fortnight was to elapse before there was any fresh information and then, one afternoon towards the end of the month, when I had called yet again at my old lodgings and was sitting with Holmes, who was still in low spirits, in the upstairs room, there came a knock on the door and a constable entered with a note from Inspector Lestrade.

After perusing it, Holmes handed it to me. It read simply: Body found in garden of empty house, 14 Leverstock Avenue, Hampstead. Would be grateful if you could attend and give assistance.

We immediately took a cab and on our arrival were met by Lestrade who conducted us to what at first sight appeared to be a bundle of old clothes, lying under a bush. It had been found, he informed us, earlier that afternoon by the house-agent who had been showing some prospective tenants over the property.

The body was unquestionably that of Juan Alberdi although we identified it less by the features than by the clothing and the gold crucifix about its neck. The method of murder, however, was immediately apparent. A knife of curious workmanship protruded between the shoulder blades, the top of the handle in the form of a small, squat figure of a man with bulging eyeballs and hideously lolling tongue.

‘Mexican,’ Holmes said briefly. ‘An Aztec design. I think we may safely assume that this murder is Gasca’s handiwork. After Alberdi sought him out, Gasca had to kill him. He knew too much.’

Lestrade greeted our news with a sombre expression. ‘At least we have a positive identification,’ he said. ‘There is precious little else to go on.’

It appeared that no one in the neighbouring houses had heard or seen anything suspicious during the previous weeks so there was no evidence as to when the body had been left in the garden, who had brought it there or where the murder had taken place.

As for the Inspector’s inquiries at the hotels, these had been almost as unproductive. There had been several likely candidates who had moved out of their rooms at about the time of Persano’s death: an elderly white-haired invalid with two male attendants, a French gentleman and his son, and two brothers, one tall and both dark-skinned, who had claimed to be Italian.

A watch on all the ports had also yielded nothing. As Lestrade had no detailed descriptions and Gasca and his accomplice or accomplices were, as Holmes had pointed out, doubtless travelling with false papers, he had very little information. It was possible that Gasca was already on the high seas, having embarked at Liverpool or some other port.

Holmes remained in low spirits for several weeks after Persano’s death and the discovery of Alberdi’s body. Indeed, it was not until the arrival one morning, at his lodgings, of a client who heralded his involvement in the curious adventure of the Ramsgate recluse and his encounter with the extraordinary Lady Studberry that he recovered his former ebullience.

As for the case of the remarkable worm, he counted it as one of his failures. Not only had he lost a friend but he had been unable, despite his great deductive powers, to bring Gasca to justice, although he never gave up hope.

As he remarked to me, ‘One day, Watson, I hope to see Gasca standing in an English court of law, charged with the double murder of Isadora Persano and Juan Alberdi.’

In the meantime, he has refused to allow me to publish an account of the inquiry. Nothing I can say has been able to dissuade him from this resolve and I have had to be content with writing out my own narrative of the case, making only a passing reference to it in the chronicles of those adventures of Sherlock Holmes which my old friend has permitted me to place before the public.*

* Mr Sherlock Holmes did indeed take up beekeeping after his retirement to Sussex. (Dr John F. Watson)

* Dr John H. Watson makes this accusation in the opening paragraph of ‘The Adventure of the Greek Interpreter’. (Dr John F. Watson)

* General Porfirio Díaz was created President of Mexico in 1876, after he led a rebellion against Benito Juarez. His dictatorship was finally overthrown in 1911. (Dr John F. Watson)

* The seeds of guarana (Paullinia cupana), a shrub native to South America, contain 5% caffeine, three times more than that found in coffee. The seeds, after roasting and grinding, are mixed with a beverage and drunk as a strong stimulant to promote wakefulness. (Dr John F. Watson)

* There are several references in the published canon to Mr Sherlock Holmes’ regrettable habit of injecting himself with a 7% solution of cocaine. He also on occasions used morphine. (Dr John F. Watson)

* Dr John H. Watson refers to the case in ‘The Problem of Thor Bridge’. (Dr John F. Watson)