He wasn't patient by nature, but when dealing with other species protocols had to be observed. He forced a smile, gritted his teeth, and knocked for a third time. "Mrs Plensca?" he said. "It's Doctor How." He fingered the wooden coat hanger, wishing he didn't need it.

The apartment door opened on a chain and two beady black eyes set on a pale face looked at him through the three-inch gap. The eyes blinked; the door closed. There were low, muttered voices in an alien language. The chain rattled and the door opened just enough for him to enter the apartment.

Mr and Mrs Plensca were as naked as the day they were hatched. Their mouths were flattened beaks, with a single nostril hole placed directly in the face behind. In everyday life these features would be disguised by a biomask; a living tissue which would give the wearer a human face. Their appearance would be accepted as well within the normal, and rather wide, range of faces in London. Its variety was one of the many features which made the city so attractive.

Beneath the translucent skin of their bodies he could make out their respiratory systems – blue-green pulsing veins squeezed between skin and organs. He didn't look any lower than chest-height. Whilst nudity in private was the norm for this particular culture, one just never knew about other taboos. The face – or at least the primary sensing area – was always a safe bet.

"You are how?" said Mr Plensca, bowing.

"Very well, thank you," said Dr How, returning the bow. "And I trust you and your lady wife are well? Do excuse me a moment." He placed the coat hanger on the door handle, unlaced his shoes, and put his socks in them. Next came his suit trousers, which he placed on the bar of the hanger, being careful to line up the creases. His jacket went on top, followed by his shirt. He slipped his underpants off and, after a slight hesitation, put them on top of his socks.

"We can help you how? Or this is a social visit during the holy month?"

"Oh. Happy Rindan holy month to you both. It slipped my mind, but then it's once every – what – three-and-a-half Earth years, isn't it?"

"Very good, Doctor. We have been here only two, so it's our first away from home," said Mrs Plensca, looking at her husband with what looked like fondness. "You observe our protocols well, for which we thank you. You would like to eat with us? My husband is an excellent... cook."

"Thank you so much, but I'm quite full." He'd made the mistake a few years ago of eating with the previous consul and her husband. Little wonder she had hesitated over the word 'cook', since the cuisine was entirely raw, and usually slimy in nature. There was an awkward silence. He beamed a smile at the couple and looked at them expectantly. They looked at each other, then back at him.

"We can help you how, Dr How?" said the consul.

"I thought I could help you."

"I assumed this was a social call."

"Ah. I received a message that your invertor was malfunctioning."

"Our invertor is functioning well, Dr How. Voltage and power are both satisfactory. We thank you for your concern."

"How odd." He turned and reached back into his jacket pocket for his smartphone. He tapped in his passcode and showed them the screen. "See? Got the message half an hour ago. I wasn't busy, so I thought I'd drop by."

"It really is most attentive of you, but we have noticed nothing."

"May I take a look?"

"By all means, Doctor." The consul waved her hand in the direction of the kitchen.

As his feet dug into the carpet he wished he'd brought disposable blue wrappers with him. Who knew what microbes or dirt he was picking up? The kitchen floor was tiled, but the sudden coolness against his feet felt awkward in a different way. He opened the fuse box and looked at the invertor. It was just as he'd installed it a decade earlier when the first Rindan consul had arrived. This was basic technology even a human could understand: it just took the domestic electricity supply and converted it to the frequency and voltage required by the occupants of the apartment. He checked the telemetry device attached to it by sending himself a test message to his phone. He pinged it back and it sent him a history. The device had not sent an alert to him. Not today, not ever. Perhaps the problem lay elsewhere?

"There is a problem, Doctor?" asked the consul.

"I wouldn't mind checking your utility cupboard, if I may." The consul nodded her assent, so he put on his underpants and opened the apartment door. The meter box was in the corridor, just outside. His feet felt even more exposed on the hardwearing blue communal carpet. This was a public space – he could only imagine what filth found its way in from outside. He squatted down and opened the door.

He heard the door of the apartment opposite open and a female voice say, "Oh!"

He twisted round and saw a middle-aged woman staring at him, open-mouthed.

"Landlord services," said Dr How. "Heating malfunction, do excuse me." The door slammed shut. He muttered to himself about social protocols and looked inside the cabinet.

The electricity meter spun steadily, and the wiring was fine. He'd just closed the door when something struck him as odd. He opened it again and checked. The water meter was turning. He stuck his head back into the apartment, where the consul and her husband stood waiting politely. Just off down the hall he heard footsteps, so he nipped back into the living room and closed the door behind him. He took off his underpants and bowed again. The Plenscas bowed.

"Do you mind if I...?"

The consul once again swept her arm.

He checked the kitchen. As he'd thought, none of the appliances were on.

"All is well, Doctor?"

"May I just use your facilities?"

"Facilities?"

"The bathroom."

"Doctor, I –"

Before the consul could reply, he raced through the bedroom. Although the door to the en-suite was closed, he could hear that the shower was on. The consul was right behind him.

"Doctor How, this is most –"

He whipped open the bathroom door. There was no one in the shower cubicle, but it was far from empty. One wall was covered in what looked like polyps – greyish-green tubes about two inches in diameter and five inches long. They drooped contentedly under the warm shower. He estimated there to be two dozen.

"Doctor How, I must protest in the strongest –"

"Mrs Plensca, what do you think you're doing?"

"I'm sorry, Doctor," said Mr Plensca. "These are my responsibility. I planted them."

"My husband was growing them for the feast at the end of the holy month," said the consul. "They're a traditional food for the final meal."

Doctor How took a couple of deep breaths to calm himself, and wished he hadn't – the smell from the polyps was not a sweet one. "Mrs Plensca, you do not have a breeding licence for these."

"We're not breeding them, Doctor," she said. "We're just growing them."

"These are an unlicensed alien species. What happens if their eggs spread into the sewer system?"

"Really, they are quite harmless, Doctor," said the consul.

"Excuse me," said her husband. He opened the door of the shower cubicle and threw some powdered food at the wall of polyps. "Feeding time," he explained.

Delicate latticed red fans flicked out of the tubes to grab at the particles washing past them. Dr How had to admit that they did look rather beautiful.

"Sexual or asexual reproduction?" he asked. "Adult or infant?"

"Unusually for such a lower-order species, they are sexual," said Mr Plensca. "This is the female infant stage."

"And no males hanging around?"

"No males."

The Doctor looked hard into Mr Plensca's eyes. "No others of this species, apart from what I see here?"

"None."

"Irrespective of your wife's status, you realise that this breach means I now have the authority to search this place from top to bottom? Or, worse still, get a Squag to do it?"

The Plenscas looked at each other, then at the Doctor.

"We will eat them all by the end of next week," said the consul.

The Doctor sighed. "Now is that the end of next Earth week, meaning a week today? Or is it next Rindan week, meaning about the middle of next month?"

"Happily, both are the same. It is end of Rindan holy month," said the consul.

The Doctor smiled and patted her and her husband on their naked shoulders, then wished he hadn't.

"Look, what I really object to is the outflow going straight into the London sewers. It's also wasteful, both of energy and water. I know it looks plentiful on Earth, but you have to remember that this is a primitive society. If you could rig up a closed system it would be much better."

"Thank you for being so accommodative," said the husband. "We must insist you have a polyp."

"Thank you, but they don't agree with me."

"No, it is tradition. You come to Rindan house in holy month, you must have polyp."

"I really must be getting back home. Lots to catch up on. Can't wait for you to prepare one."

"No preparation needed, Doctor. Eat raw. Like... Like oyster."

"Oysters are a bit smaller. One gulp. These look... big."

"Yes, you must take one, Doctor. Bad luck if you don't." Mrs Plensca left the bathroom.

"Here. This is nice one," said Mr Plensca. He reached under the spray and touched the foot of a polyp. The whole mass of polyps shrank back against the wall, their orifices shrinking small and tight, like a tapestry of anal sphincters. He peeled the base of one away from the tiles as his wife came back into the room holding a Tupperware box, which she handed to him. He let some of the warm spray fill the box and then put the tight polyp in it. He presented it to Dr How with a bow.

"Thank you," said the Doctor.

"It must be eaten in the next six hours," said Mr Plensca, "Otherwise it will begin to go off."

"I can't imagine how bad that would smell," said Dr How, to puzzled looks from his hosts.

The three of them went back through to the living room and the Doctor hurriedly put his clothes back on. "Well, thank you again for the polyp," he said.

"It was nice to see you, Doctor," said the consul.

"Enjoy the rest of your holy month."

The door closed behind him. He stepped to one side, put the coat hanger and Tupperware box down and took his shoes off. He leaned back against the wall, removed the sock from his left foot, took out a hygienic wipe from his pocket, unwrapped it and rubbed it over the sole of his foot. He put the sock back on and put his left foot back in the shoe. He was wiping the sole of his right foot when the door opposite opened again. The middle-aged woman stared at his bare foot, the coat hanger, and the Tupperware box.

"Germs," he said. "You can't be too careful, can you?"

 

He made his way out of Du Cane Court and up Balham High Street without further incident, coat hanger and Tupperware box in hand, then turned right at the combined Tube and overland station. On Sundays the service was half-hourly, which was too long to wait for such a short distance, so he walked up past Tooting Bec Common. Murphy's Law being what it was, a couple of minutes later a train rumbled its way up towards Streatham Hill, with a couple of pistol-shot reports as the train went over the points and the electricity sparked from the third rail.

A couple of green parakeets squawked loudly as they flittered between trees. They were another invading species that had been introduced unintentionally – no one knew exactly when, or by whom. Whilst they added an exotic air to the parks and gardens of London and Kent, they played havoc with the indigenous wildlife.

There was still no explaining the invertor, and he wondered if the Plenscas might think it had been a ruse to enter their apartment. His apartment, he reminded himself. He was, after all, their landlord. And he did have other caretaker responsibilities – not just to other consuls and out-of-towners in other apartments throughout London. A look to his right was the only reminder he needed as to why this was such a plum posting: lush grass and old oaks. Even the railway embankment was teeming with life.

He took a deep breath. A delicious twenty-one percent oxygen, mixed with unreactive gases. A strong but reasonable gravitational field, giving a decent pressure and thus a habitable temperature range for any water-based species – which was most of the known universe. Or, at least the known Pleasant universe. He had a predilection for trips to Earth's Carboniferous period, for the thirty-percent oxygen content and the sight of the gargantuan insects it supported – dragonflies three feet long and multi-coloured butterflies with six-foot wingspans being his favourites.

The invertor. He mulled it over. It hadn't sent a message. What, or who, had? A rogue message was highly unlikely. Conclusion? He'd been hacked. By whom? Or was it by Who? Unlikely, if not impossible at the moment.

He walked on, up the gentle slope and into the Telford Park Estate. He'd bought one of the solid red-brick Victorian houses off-plan from Telford himself, some thirty years after the railway had arrived in Streatham Hill. Nothing too extravagant – just a semi-detached. It was spread over three floors and a cellar, with three receptions and five bedrooms. He liked the castle-like appearance of the design – the front of the house had a faux turret and the roof sloped into crenellations, rather than guttered eaves. Spacious enough for his needs, but nothing that would attract too much attention in that kind of neighbourhood. Mr Telford had been surprised at the modesty of the Doctor's choice, given the substantial sum Telford had just paid him for this, the last enormous parcel of Doctor How's land.

It had been one of his longer-term investments – over eighteen-hundred years – having bought it in AD43 as the Emperor Claudius' troops invaded Britain to reinstate Verica, exiled king of the Atrebates. There was nothing like war to devalue the price of real estate, and the previous owner had been only too happy to be able to take the gold and flee north. Few things do more for the value of land than the enforcement of the rule of law, so although he had to pay a higher tax to the Romans he was happy to do so as the rent he received more than covered his initial investment. He'd not needed to visit much in the Dark Ages that followed – just the odd scare with a few projections. The Black Death had proven tiresome owing to a shortage of competent administrators but the rest, as they say, was history.

The Doctor didn't need all that land and the wealth that came with it. However, he'd always felt that it was important to have a genuine sense of attachment to a place. It gave him something to bat for, and he enjoyed seeing the development of cultures over such long periods – the changes in customs and religions, the evolution of language and the inexplicable, nonsensical fashions. And the people – although he was essentially a loner, he did love to meet the great and the good of each period, as well as the ordinary person on the street. For him, the game of fantasy dinner-party guests was played for real. And having the land and wealth of the well-heeled made it so much easier to be accepted, and to entertain. He was fondly remembering a dinner with H. G. Wells when he came within sight of his house.

Old Mrs Roseby was in her front garden, pretending to water her roses. His heart sank.

"Good morning, Mrs Roseby. Lovely day, isn't it?"

"Good morning, Dr How. Rain expected later."

He cast a deliberate look at her tin watering can, drawing her eyes to it.

"You can't be too careful with roses at this time of year. Besides, the weather girl looked foreign. Them foreigners don't know the British weather so well, do they?"

"It's all done by computers, Mrs Roseby. Big computers. She's just a presenter."

"Don't trust them computers either. When I was a girl –"

"When you were a girl, the very first proper computers saved the free world by breaking the Nazis' secret code, Mrs Roseby. Trust me, it'll rain later. And roses really don't need that much water. Deep roots. Now, was there anything else on your mind?"

The old woman put down her can, its clang on the brick path betraying its emptiness. "Your dog frightened the life out of my Albert."

"Albert the cat?"

"Yes. Poor thing nearly had an 'eart attack. Your dog slammed up against the door and barked and snarled like a... Like a..."

"Like a guard dog?"

"Yes! Like a guard dog."

"Well, that's reassuring."

Mrs Roseby was confounded, so he moved further down the path to his front door. She shuffled after him on her side of the wall.

"I've never seen that dog in all these years," she said. "You ought to let it out for exercise. That's why it's so ferocious. It's a miracle it doesn't eat that cat of yours."

"Two salient points to bring to your attention, Mrs Roseby. First, my apparently ferocious dog has not eaten my cat after all these years. Second, would you really want a ferocious dog out on the street?"

"Well, I... I... You never even let him in the garden."

"He's agoraphobic. I'll have a word with... With Bonzo. He'll be quieter in future. I promise. Good day, Mrs Roseby." He put his key in the lock and turned the brass handle. The handle felt just a touch different. He sniffed his hand and concentrated. Fried food and human hand-sweat, plus an undertone of cheap soap. He'd had a visitor. An unwanted one, by the sounds of it. He took a sterile bud from his pocket and rubbed it all over the handle, then popped it in its matching test tube and put it back in his pocket. He'd get the DNA analysis later. He pushed a button and the UV disinfecting lights on the sides and ceiling of the porch came on. He gave himself a five-second twirl in their invisible rays. His white shirt glowed a pleasing blue colour. The door to the house was open, and he closed it after entering.

"Trinity," he called.

A large black cat with the musculature and movement of a panther padded down the stairs and across the polished oak floor. It rubbed against his legs.

"Mrs Roseby tells me you've been quite loud. She's probably listening for an over-excited dog right now."

The cat looked up at him with her green eyes and gave two deep, throaty barks which reverberated around the hall.

"Good girl. Now, is this who came to call?" He presented the palm of his hand. The cat sniffed it and gave a miaow of assent.

"I wonder if that's the same person who hacked us, Trini." The cat tilted her head.

"Yes, I think we've been hacked." The cat hissed and stuck her tail in the air.

"Oh, we'll get him, don't worry about that. Now, I've brought you a little treat from the Plenscas. How do you fancy a bit of raw Rindan polyp?" Trinity gave a loud growl and followed him through to the tiled kitchen, rubbing against his legs.

He set down the Tupperware box in Trinity's eating area and she purred as he removed the cover and presented it with the foot of the polyp facing her. The polyp pulsed, feeling the surge in available oxygen. Its red fan flicked out into the air. Trinity looked at the Doctor, then sniffed the creature's foot. It shrank to half the size. If a cat could have shrugged, that's what Trinity did. She bit the foot and the creature squeezed itself tighter. In a couple of swift movements she had just the top of the polyp showing in her mouth. It flicked out its red fan beyond Trinity's nose and she caught it in her teeth. She gulped down hard, then opened her mouth to show Dr How the red innards, which had been pulled out from the body. She chewed the innards and the fan.

"Oh, that's the best bit. I see. Clever girl."

He put the Tupperware box in the dishwasher and washed his hands with disinfectant soap.

Trinity licked around her mouth and sat back, purring. He stroked her head and she pushed back against the palm of his hand.

"Oh, my dear Trini," he said, "I have a feeling we're going to be terribly busy very soon." She looked up at him and gave him a low, questioning growl. "Oh, I just know."