Lily clasped Malkin close to her chest. A whoosh of wind pounded around them, feathering Malkin’s fur and blustering against her face.

There was a ripping sound and she looked up anxiously. Where it was rubbing against the anchor line, the mail sack had begun to tear open at the seams, unravelling under their weight.

She swallowed back a lurch of panic and fumbled with her numb fingers for the metal clip, clasping it just in time. The bag whisked away beneath them, blowing across the sky like a kite in a gale.

Her grip tightening on the clip and her other hand round Malkin, Lily sped down the line.

Branches swished past and the moonlit lake streaked towards her, the dropped box floating in its centre. She was only a few feet from the water now… Malkin gave a loud growl, but didn’t let go of the locket, and then—

SPLAAAASH!

They were in.

The water gurgled ice-cold around them, deep as the sky above. Lily tried to pull herself to the surface, but she couldn’t tell which way was up. She choked for breath, and struck out for a shimmering reflection of light, thrusting with her legs and arms. Pushing her head high, she broke the surface near the bobbing box and threw Malkin up onto its lid.

He’d barely been in the water more than a few seconds, and seemed all right, thank tock. He shook the water from his fur and gave her a most disgusted look.

She was about to apologize when, with a gigantic splash, another mailbag containing Robert fell into the water beside her.

“Clattering clockwork!” she cried, as she pulled him free from the tangled sacking. “There you are! Grab onto the box!”

She thrust the box towards him and its corner knocked against his head. He grasped it with one flailing arm, laid his cheek upon the lid like it was a float, and took a deep breath.

“For a second it felt like I was swimming in the air and flying in water,” Robert spluttered.

Malkin spat the locket out into his hand. “How poetic,” he groused, pacing the lid of the box. “But the unvarnished truth is we all could have drowned. Me especially! So far on this trip I have been stuffed in a suitcase and thrown from a moving airship. From now on in, I shall listen to neither of you jangling idiots. However cunning you might protest your plans to be!”

Robert tried to ignore his moaning and instead concentrated on getting the locket over his head and back around his neck.

“Stop shifting about, you meat-muppet!” the fox growled. “You’re rocking the box! You’ll tip me in. Don’t you know foxes hate water?”

Robert pushed the locket beneath his wet shirt and spat out a mouthful of silty slosh. “You’re nothing like a real fox.”

“Then mechanimals HATE water,” Malkin said. “It messes with their insides.”

“It messes with my insides too,” Robert cried.

Lily ignored them, looking instead for the Doors. With relief she realized they’d not followed. Understandable really. You’d have to be crazy to jump out of a nice warm moving airship into a freezing pond, especially if you didn’t like to swim.

Someone had cut the line and the zep was floating freely again, over the hills towards London. Time to make for land.

“Thrash your legs – like this,” Lily told Robert, grasping the corner of the box and pushing the three of them towards the edge of the lake.

Robert did as he was told, kicking along with her. When he finally looked up, they were closing in on the bank. He was getting the hang of this swimming lark, even managing to keep his eyes and nose above the waterline – though not his mouth, unfortunately.

They reached the shallows and Malkin leaped daintily from the lid onto the bank; barely a drop of water had touched him.

Robert flopped down on the muddy incline and guzzled the air. It was good to feel the earth beneath him once more. Sky was one thing, but water quite another.

Lastly, Lily clambered out onto the lakeside and stood shivering, her skin goose-pimpled and cold. The box grazed against the bank, making horrible sludgy sucking sounds.

“Well,” said Malkin, “at least we’re all still in one piece. I thought I might crack up for a second.”

Lily nodded. Then she realized something. “The Doors have our bag! It’s still in the airship! It has the Queen’s Crescent envelope, the inspector’s card and Papa’s address at the Mechanists’ Guild. They’ll know everywhere we’re going.”

“At least we still have the Moonlocket,” Robert said. So why did it feel as if they had lost the battle and the war?

He scrambled to his feet and brushed a hand across his wet face. His cap was gone! Then he spotted it floating on the surface of the water by the shoreline, a few feet away. He picked it up and stuffed it back on his head. It dripped drops down the back of his neck.

They seemed to be on a heath at the outskirts of a village. Far off, he could see the odd twinkle of a street lamp, and the London skyline edged in the orange glow of the rising sun. The zep was floating above it, dipping towards the tall spired clocktower of St Pancras airstation. The Doors would reach the city far before them, with all their possessions. “We have to do what they’d least expect,” he said at last.

“How?” Lily asked.

“Well, they probably think we’ll head straight to the police, or your papa, so we should go to Queen’s Crescent first.”

“And confound their expectations, you mean?” Lily wrung the water from her dress. “I suppose it’s the only advantage we have.”

“And the locket. Don’t forget we have the locket!”

“Much good it’s done us,” Malkin muttered.

They stumbled downhill and along a path that took them to the edge of the heath, the early morning light warming their backs. Lily’s belly made empty, gnawing complaints and her head was void of ideas. Her cold wet clothes clung to her skin, tugging on her limbs and weighing her down. She took out her pocket watch, but the hands were stuck at four thirty.

It must’ve stopped when they fell in the lake. That being so, it was a miracle that Malkin was still working. Thank goodness she’d fished him out of the water when she did!

She tried winding the watch, but it only made a sad clicking sound. She would have to remember to ask Papa to fix it once they were all home again. Or Robert. She glanced over at him. His brow was furrowed with worry.

How would they ever find his ma in time to warn her that Jack was looking for her? Lily wondered. All they had to go on was a single street name for a place where Selena had lived years ago.

The trees thinned and they reached the edge of the heath, where a railway bridge crossed over an empty branch line. On the other side of the railway tracks was a street of tall houses.

They crossed the bridge and, as they ran down the steep set of steps on its far side, a boy turned the corner sharply at the bottom and began coming up the other way. Lily crashed straight into him.

“Careful!” the boy admonished, but it was too late. He’d dropped his pile of newspapers. They scattered on the floor around them.

“Oh my goodness!” Lily muttered, and she stooped and began to help him pick them up.

Robert joined in, and Malkin tried too, but some compulsion made him tear at every paper he took in his mouth.

“Your dog’s ruining my early editions!” the boy cried. “They’re only just hot off the press!”

“Sorry,” Robert said, and he tried to pull the pages from Malkin’s mouth.

Lily joined in with the tug of war, but the newspapers were fast becoming a shredded mess. They floated like confetti to the ground, until all that was left in her hand was the masthead banner – The Daily Cog.

She handed that paper scrap back to the boy, apologizing again. He stuffed it under his arm, along with the few issues he had managed to protect.

“Sorry’s no good to me!” he whispered mournfully, staring at the shredded sheets with a tinge of disgust, and scratching his thatch of curly brown hair. His tanned face, covered in roadside dust, looked utterly disheartened. “Sorry don’t bring nothing back.”

“Oh,” Lily replied. Then she noticed that his clothes looked rather threadbare. His bony elbows were practically poking through the sleeves of his raggedy shirt.

“What happened to you, anyway?” the boy asked, giving them the once-over. “It ain’t raining but you look like you’ve been in the cats and dogs. You’re all wet.”

“Let’s just say we fell in a pond on that heath and leave it at that,” Malkin muttered.

The boy brightened. “Well I never!” he said. “Your dog can talk. Is he a mechanimal then…? Looks almost real.”

“I’m a mechanical fox, I’ll have you know!” Malkin gave a snort of derision, but that didn’t stop the boy’s questions.

“Right-o!” he said. “And what were you all doing in Highgate Ponds? Taking a dip, I suppose? Most people bring a bathing suit for that, or they’re in the altogether! You lot look like you jumped in with all your mufti on. Besides I thought mechs and swimming didn’t mix?”

“They don’t,” Malkin said. “Neither do mechanimals and airships.”

“We fell out of an airship,” Lily explained. Although the boy now looked even more confused, and she realized it probably wasn’t much of an explanation.

“Look, can we move on?” Malkin said. “It’s been clattering good fun – all this biting and running, jumping and drowning, and bumping and chit-chat, but where are we actually headed?”

Robert stepped away from the boy, who was still fussing with his papers, and touched the locket around his neck. “Queen’s Crescent, Camden, remember?” he whispered to the other two. “I don’t suppose either of you have any idea how to find it?”

Malkin tutted. “Perhaps we should’ve thought of that before we left?”

Lily felt downhearted. If it hadn’t been for Jack forcing them to rush from the house last night, they probably would have thought to bring a map. “It’s no use,” she muttered darkly. “We haven’t a clue where we’re going.” She turned around, and was about to ask the paper boy if he knew any such place, when she saw that he’d stopped picking up his papers and was eavesdropping.

“Queen’s Crescent is only twenty minutes away,” he said, his hazel eyes glinting. “For a penny, I can show you the fastest route. That’s if you’d like?” He gave her a smile, and his cherubic cheeks dimpled at the sides as he watched Lily fish the coins from her purse.

“Name’s Bartholomew Mudlark, by the way,” the boy said. “What’s yours?”

“Nice to meet you, Bartholomew,” Robert said. “I’m Robert.”

“Bartholomew’s a bit of a mouthful, so most people call me Tolly.” Tolly wiped the newsprint from his hands on the tails of his coat and shook Robert’s hand, and then Lily’s.

“Pleased to make your acquaintance, Tolly,” Lily said. “I’m Lily, and this is my pet mechanimal; he’s called Malkin.”

Malkin offered Tolly a muddy paw and a friendly yap.

Tolly stuffed his papers in his canvas bag, and slung the strap over his shoulder. “All right,” he said. “That’s the introductions over, so let’s be off…”

He crooked out his right elbow for Lily, as if they were about to step out together for a promenade. After a moment’s hesitation, she looped her arm through his and they set off down the street, with Robert and Malkin following behind.

The sun was almost fully up and the sky bright. The early morning air had a pleasant brisk quality to it and a light refreshing wind blew about them, throwing up the odd gust of dust. They dripped water as they walked the pavements of Camden, the wind and sunlight slowly drying them off.

“What are you looking for in Queen’s Crescent?” Tolly asked as they strolled along.

“Clues to a mystery,” Lily explained.

“That’s exciting,” Tolly said. “I enjoy a good mystery, me.”

“Why?” Robert asked. He wasn’t sure yet just how much they should tell Tolly, or whether they even needed another companion.

“I dunno. Just find them gripping. ’Specially the penny dreadfuls – sell a few of them on occasion. Full of intrigue, they are. I always dreamed of getting involved in some skullduggerous adventures like that!”

“Then you’re in luck,” Lily told him. “We’re slap bang in the middle of one and it’s a wealth of trouble!”

“How so?” Tolly asked.

“Well,” she explained. “We forgot our map of London, lost our luggage, were chased by the Jack of Diamonds and, to top it off, we don’t know where we’re going. But we’d be glad to have someone as clever as you along, Tolly, to aid us.”

Tolly looked pleased as punch about this. “That’s a proper frightful story, and no mistake,” he said. “If the Jack of Diamonds really was after you, then you’re lucky to be in one piece. Naturally, I’ll do my bit to help you, as best I can. Which, I might add, will be considerable – since I know this area like the back of my hand.”

“Thank you,” Lily said, cheerily. She felt pleased to have stumbled on such an ally, and relieved that he had evidently taken a shine to her. London felt a huge and scary place to navigate on one’s own, despite them having visited once before.

Malkin didn’t say anything, and neither did Robert. He was still a little unsure about Tolly, but they did need help, he decided.

Tolly seemed much more concerned with putting them at their ease than making further enquiries about their predicament. He took inordinate care to point out all the little things they passed on their journey and offered up explanations of every one.

“There’s the fountain where the pigeons congregate…” he said, of a disused horses’ water trough. “And there’s old Pete the sniffling lamp-snuffer,” he added, nodding at a man carrying a long stick with a tin hat on the end, who was dousing the street lamps. The man gave Tolly a snort of recognition.

“And here comes Artie, the knocker-upper, getting folks out for the daily grind…”

The rows of detached red-brick houses had become low terraced cottages. They saw a man with a pea-shooter, shooting peas at the top-floor windows to wake people for work.

“How do you know everyone?” Lily asked. “Are your family from round here?”

“Nope. I’m an orphan.”

“So where do you live?”

“At the Camden Working Lads’ Mission,” Tolly explained. “They took me in when I was young. I’d run away from the poorhouse, see? And got into a bit of crime…but the geezers at the mission rehabilitated me. Taught me to read and write, from old newspapers mostly, and then they found me gainful employment. In return I got a roof over my head – I share a room with four other lads. It’s a bit of a squeeze but I prefer it to the poorhouse. And I like selling papers – it’s much better than washing smalls in the mission laundry, because I get to read while I work. I like the investigative stories best…”

Lily could barely imagine what that sort of life was like. She was relieved she had a home, and didn’t live in a whirlwind all the time as Tolly seemed to. He even walked as fast as he talked – not slowing for anything, kicking his feet up high as he strode along, and chatting all the time. He stopped only once at an old drain cover, leaning down towards it.

“Listen,” he said. “D’you hear that?”

“Water!” she cried in delight.

Tolly nodded. “This road we’re walking on used to be part of the Fleet River. It ran from Highgate Ponds – what you fell into on the heath – right under these cobblestones and Queen’s Crescent, and then flows onwards through North London, all the way down past Fleet Street – that street was named for it – along Farringdon Street, and finally tumbles into the Thames near Blackfriars Bridge. My grandfather used to sail down it, transporting stuff on the longboats.”

“But where is it now?” Lily asked. “A whole river can’t just disappear.”

Tolly shrugged. “Bazalgette and that lot paved over it.”

“Bazalgette?”

“The fella who built the London sewer,” he explained. “The Fleet’s part of it. Flowing underground. Instead of boats, it floats sewage downstream. Pretty profitable for him, I heard. But you know what they say – ‘Where there’s muck there’s brass’.” He laughed at his own joke, and Lily decided she’d better join in, out of politeness.

Robert couldn’t hear much of what Tolly was saying, because the other boy was walking too fast. He and Malkin had to hustle to keep up. But he was thinking about other things in any case – whatever clue might be at Queen’s Crescent, Robert was worried that Jack would have got to it first. And even if they made it to Lily’s papa at the Mechanists’ Guild, there was a good chance Jack would show up there too. So far, it seemed as if he’d been one move ahead of them every step of the way.

Finally they turned into another street lined with elm trees and, behind them, flat-fronted houses coated in white rendering, like cracked royal icing. Every house was framed by wrought-iron railings and a worn set of stone steps led up to each front door.

“This is Queen’s Crescent,” Tolly announced. “What number are you after?”

“We’re not exactly sure,” Lily admitted.

“I see.” Tolly’s face creased in confusion.

“I think their plan is to knock at each house,” Malkin sneered. “If there’s any other way to announce our presence more blatantly, I’d like to know what it is?”

Robert shook his head. “We don’t need to knock on the door of each house. I can remember what it looks like from the picture.”

He began to walk up the road. A lot of curtains were still drawn, but people had decorated their windows with bright red and white flowers and blue bunting in preparation for the Queen’s Diamond Jubilee in two days’ time. All the homes were very smart, but then the one in the photograph had been too, Robert remembered, with its jolly little apple tree in the front yard.

He stared at each place in turn, waiting for a sign of recognition, and yet none came – until he arrived at the scruffiest property on the street. Trailing vines of dead ivy hung from its guttering, fringing dusty, rotten-framed windows.

“This house needs a haircut,” Malkin muttered.

“And a fresh bit of slap,” Tolly added.

Robert frowned. He was inclined to agree, but there was something about the place – even in its run-down state – that looked remarkably similar to the photograph in A Popular History of Modern Magicians.

He peered between the broken railings; the front garden was a spiderweb of cracked concrete and weeds, and growing among them was an ill-tended, scraggy apple tree. It had only a handful of hard little apples, and a few wilted leaves, but he remembered it blooming in the photograph. He looked up above the green flaking front door and found the plaque with the street name, hidden beneath the dead ivy and screwed to the side of the house.

“This is definitely it,” he said. “The Door family home.”

At least, it had been once, a long time ago; now it was no longer. His ma had lived here in her youth, he knew that much. And he could only hope that she’d somehow left another clue to help him find her – like the rest of the locket perhaps… Instinctively he reached for the chain around his neck, then pulled his hand away. It was his “tell” Jack had said, and though the house looked dark and empty, someone in there might still be watching. “I do hope this isn’t a trap,” he said quietly to himself.

“You mean a trap Door?” Malkin butted in.

“It’s rather early to be paying calls,” Lily reassured them both. “That’s probably the only reason it’s so quiet…”

“Blimmin’ heck,” said Tolly. “You really do reckon the Doors are after you, don’t you? Do you want me to do the talking? Whoever’s in there won’t know me from Adam. I can say it’s a newspaper delivery…”

“No. No, thank you,” Robert interrupted. “I’ll be fine on my own. Don’t worry. I don’t think they’ll be here yet anyway. And besides, I’ll think of something.” He threw his shoulders back and, with more confidence than he felt, jostled past them and strode up the garden path.

As he climbed the steps to the entrance, his guts gave a twist. The stone steps had worn away and the number forty-five was daubed in dripping white paint on the glass of the transom window above the front door. He took a deep breath and reached for the knocker.

There was none. Nor a letter box. So he knocked instead, three times, on the peeling panelled door with his fist, and waited for someone, anyone, to come and answer…