Robert was running out of time. The hour of the professor’s party had almost arrived. The guests were due to start turning up any moment and he needed to get changed for the evening’s events. The trouble was he still hadn’t finished repairing Lily’s birthday present.

He’d always intended to have the pocket watch mended by her fourteenth birthday at the very latest, and to give it to her as a surprise. But here he was, still working on it at the eleventh hour. And here the watch was, still not working.

At least Malkin had stopped gnawing at his trouser leg – that was one less distraction. Though the threadbare old clockwork fox was still curled up beneath his desk, getting under his feet.

“What’s taking so long?” Malkin asked, blinking his black eyes. “You said you’d be finished by now.”

“One more piece…”

Robert peered down through his magnifying glass at the watch’s interior. The hairspring, gear train, balance wheel, fork pin and escapement mechanisms were perfectly balanced and aligned, like a miniature landscape. On the top edge of the case, beneath the crown, was the maker’s mark: T.T. – for his da, Thaddeus Townsend.

The pocket watch had been made by Thaddeus years ago and Lily’s papa had bought it and given it to her on her ninth birthday. But the calibre inside the case had stopped when he, Lily and Malkin had fallen into the Fleet Ponds on Hampstead Heath after jumping from a moving airship, and since that day Robert had taken it on himself to repair it.

He’d spent months cleaning every interior element of the watch and now he had only to replace one last jewel bearing that balanced the pivot wheel. He took up his tweezers and carefully picked the tiny glinting gem up from his desk.

His hand shook as he held it over the watch case and teased it into place.

“What’ve you got Lily?” he asked Malkin, more to distract himself than anything else.

The fox drew back his lips, revealing yellow teeth. “I shan’t tell you. It’s a surprise.”

Robert wondered if that surprise was the dead mouse he’d seen Malkin nudging around the dusty corner of the hallway the other day, but didn’t dare ask.

The bearing slipped smoothly into its fixing, slotting in with the other parts. Robert closed the watch case over it. There. His work was complete.

His belly fluttered with excitement as he wound the watch for the first time and brought it up to his face. He could hear the tick of the parts in the calibre and the hands moved smoothly, just as they should.

He set the time by his new mantel clock, then slipped the watch into an envelope, which he tied with a red ribbon.

Now he could give it to Lily as soon as he saw her.

He stood and changed quickly into his outfit for the evening: a dress shirt, sharp black trousers and shoes that shone bright as buttons.

He tucked away his ma’s silver Moonlocket that he always wore beneath his shirt collar, before tying his bow tie and finally adjusting his cog-shaped cufflinks.

Then he pulled on a long-tailed, silk-lined suit jacket and put the envelope containing the watch in its pocket, before stepping over to the full-length mirror next to the washstand to admire himself.

He didn’t scrub up half bad. The suit still fitted, just about. He’d worn it to the Queen’s Diamond Jubilee in July, and for his own birthday last month. Though it had got a little short in the sleeve since then, he observed. And his reflection now grazed the top of the mirror.

With delight he realized he must’ve grown. Perhaps he was destined to be the most statuesque one in his family? His da hadn’t been particularly tall when he’d been alive, and his ma and little sister, Caddy, who he’d first met over the summer, had both turned out to be rather dainty in stature. Currently the pair of them were travelling the world performing in their spiritualist show, and though they’d promised to return soon, Robert wasn’t sure how long that would be. He wished they could see him now. Fourteen years old and looking practically a man in his smart suit…carrying on Da’s work, an’ all – how proud they’d be of him!

Though his hair was still a mess… He reached over to the washstand for a glop of pomade and ran a hand through his tangle of curls, trying to straighten them out.

It didn’t work. The hair sprang back almost immediately, its unruly spirals twirling round the tips of his ears like overenthusiastic ivy. He gave up and, after washing his hands in the basin, straightened his bowtie instead.

When he’d finally finished, he did up the breast button on the front of the suit.

“How do I look?” he asked Malkin, who was now rustling the tissue paper in the suit box that lay on the bed, trying to make a nest with it.

The fox gave a black-lipped sneer and wrinkled his threadbare nose. “Like a penguin who’s just lost a job as a waiter.”

“Thanks.” Robert contemplated trying to wrestle a ribbon around Malkin’s neck. Partly in honour of the evening’s occasion, and partly in revenge for his snide comment. Then he remembered how sharp and snappy Malkin’s teeth got when he was angry and thought better of it.

“I think Lily’s hiding from us,” Malkin said. “Or sulking. You know how bad she gets when she thinks no one’s paying her any attention, and that’s when it’s not even her birthday. Clank knows what she’ll be like tonight, with a party where she’s not the main event. At least we’ve got our gifts to cheer her up. You’ll carry mine for me, won’t you, Robert?”

Malkin jumped off the bed and nudged something small and furry towards him along the floor. It was the very dead mouse Robert had feared. “I’ve no opposable thumbs, you see.”

“All right.” Wearily, Robert picked up the deceased rodent and put it in his pocket. He found it best not to argue with the fox in cases like this.

At least Lily would be pleased with his present. He was pretty chuffed himself with how it had turned out. His clockmaking skills were improving and one day he would be a master horologist, just like his da. He was, he realized, gradually becoming the sort of person who could put anything back together. No matter how broken it might be.

Downstairs in the hall, all the lamps were lit and the front door was open. Lily was nowhere to be seen, but in the foyer the first few visitors had already materialized. Outside, in the glowing sunset, a queue of hansom steam-cabs waited to disgorge the rest of the guests onto the front steps.

Professor John Hartman, Lily’s father, was standing in the vestibule, shaking hands and bowing politely to each and every new arrival as they entered the house. When he glimpsed Robert and Malkin at the base of the stairs, he surreptitiously beckoned them over.

“Have you seen Lily?” he asked.

Robert shook his head. Malkin shook his snout.

“That’s a shame,” John said. “She’s missing out on all the fun.”

What fun? Robert wanted to say out loud, and he was surprised that for once Malkin didn’t say it for him.

By now the entire hall and front parlour were packed with fusty, dusty-looking professors from the Mechanists’ Guild. Robert knew they were from the guild because each wore a single golden cog insignia – the guild’s symbol – pinned to their coat lapel. And he knew they were professors because they looked professor-y – which is to say, rather rumpled, eccentrically dressed and a little wild round the edges. He searched for a friendly face among them, but there was no one he knew.

John observed his look of scepticism. “I invited some of Lily’s pals – that reporter, Anna Quinn, and her assistant, Bartholomew Mudlark.”

“Where are they then?” Malkin queried.

“I don’t know,” John replied, “but they promised to put in an appearance. This lot have flown in on the evening transport zep, but Anna’s probably bringing Tolly in her own airship.”

“You mean Ladybird?” Robert asked.

“That’s the one.” John nodded. “After they’ve arrived, and when the presentation part of the evening’s over, I’m going to give a little speech for Lily at around nine and give her her birthday gift in front of everyone.”

He pulled two small packages from his pocket and showed them to Robert and Malkin. They were both beautifully wrapped in colourful paper and red ribbon. “They’re a surprise. So if you wouldn’t mind keeping them a secret until the big moment arrives? You too, Malkin – I know what you’re like.”

“Of course,” Robert said.

“No matter what,” Malkin yapped.

“Thank you.” John smiled. “In the meantime, go see if you can discover where Lily’s got to. Try to cheer her up a bit and get her to come down, eh?”

“I’ll do my best,” Robert said.

“As will I,” Malkin agreed. But as they wandered off, he added, “I imagine she’ll need a great amount of cheering when she hears the quality of the guests who’ve arrived so far.”

They decided to start the search for Lily in her bedroom, but when Robert knocked and put his head round the door, he found that, apart from the clothes thrown across the floor and the stacks of gothic novels that adorned the bookshelves, the room was empty. He checked under the bed, in case she was hiding from them there, but she wasn’t.

As he stood up he knocked the bedside table, toppling over a small fossil. He set it carefully right as best he could. The fossil was an ammonite of fool’s gold embedded in a stone that Lily’s mama, Grace Hartman, had found on a beach and given to her daughter. Robert knew it was one of the last gifts Lily had received from her and as such it was extra-special. Lily had told him that Grace had been a keen amateur geologist, as well as one of the first female mechanists in Great Britain.

The library was next, because Lily sometimes liked to sit in there and read, but it too was empty. As were the other upstairs rooms, and the servants’ quarters, which they hadn’t really expected her to be in anyway, seeing as Mrs Rust and the others weren’t there for her to talk to.

Finally, Robert suggested they try their den at the top of the tower.

Malkin complained loudly as the pair of them climbed the stairs to reach the topmost room. “There’s too much winter damp up here. It rusts my insides. Seeps into my springs.”

“John’s asked that we find Lily, Malkin,” Robert said. “And anyway, it’s either this or talk to those boring professors for hours – which would you prefer?”

“Well, when you put it in those terms…”

They stepped into the tower room and there was Lily, sitting in the scruffy old armchair. Her long shadow stretched across the dusty floor in the last yellow slivers of fading sunlight. In her hand she held a red leather-bound book, which she must’ve been reading, but she slammed it shut as soon as they arrived. From the look on her face, Robert guessed she’d overheard everything they’d been saying.

“What’re you doing up here?” he asked.

“Sulking,” Lily said. “D’you want to know why? Because it’s my birthday and everyone’s ignoring me. Rushing around after Papa, who’s behaving as if he were the Queen of Sheba. And now the house is full to the brim with those awful old mechanists, who are no fun at all. There’s no one for me down there.”

“That’s not true,” said Malkin. “If you’d bothered to ask instead of moping around, you’d realize there are guests coming for you.”

“Who might they be?” Lily asked.

“Anna and Tolly,” Robert replied.

“Really?” Lily leaped from her seat.

“They’re not here yet,” Malkin said.

“Oh.” She sat back down on the arm of the chair and hugged her book despondently.

The gold pattern embossed on the cover glinted. It looked like an ammonite, Robert thought. “What’s that book?” he asked.

Lily opened her mouth to reply, but then seemed to think better of it. After a moment she said, “It’s either nothing, or you’ll-have-to-be-a-lot-nicer-to-me-before-I-tell-you.” She hid the red notebook behind her back. “The choice is yours.”

“In that case,” said Robert, “you won’t be wanting the birthday presents we’ve brought you.”

“I didn’t say that, did I?” Lily replied with a wry smile. She leaned back in her seat and folded her arms, waiting to be impressed.

“What’ve you brought me?”

“Give her my gift first, Robert,” Malkin commanded.

Robert reached into his pocket and apologetically handed over the perished rodent.

Lily took it in her palm and gave it an unsavoury stare. “It’s certainly…different. I mean, it’s not like anything I’ve been given before.”

“I thought you’d like it.” The fox ran his long pink tongue round his whiskers. “Keep it safe. A lot of thought went into that.”

Lily shrugged. Robert watched as she reluctantly put the dead mouse away in the pocket of her dress.

“Where’s your present, Robert?” Malkin yapped.

“I have it somewhere.” Robert made a show of searching through his jacket. “I’m just not quite sure where… While I’m looking, d’you want to see a new trick I’ve learned?”

“You’re certainly dressed for it,” she retorted. “You look like a proper stage conjurer in that outfit.” She checked herself. “I’m sorry. I didn’t mean…”

“That’s all right,” Robert said. Half his family – the bad half – had been magicians. He didn’t really like to think of them. But his ma and sister, who’d given him his Moonlocket, were theatrical mediums. They wrote letters sometimes, telling him about their enchanting escapades as they travelled and performed alongside conjurers and the like, and ever since he’d started corresponding with them, magic was an interest that had grown in him.

“Oh, I know where it is!” He tapped Lily’s dress pocket on the opposite side from the dead mouse. “Have a look in there.”

Lily put her hand in her pocket and pulled out an envelope tied with red ribbon. “How did you do that?” she asked, astounded.

Robert grinned. “A little bit of sleight of hand. It’s the same as picking pockets, except you put something in instead of taking it out.”

“What’s in the envelope?”

“Open it and see.”

“It feels heavy.” She tore along the side of the envelope and tipped the pocket watch into the palm of her hand. “You fixed it?”

Robert nodded.

Lily examined the watch, her wide, excited eyes reflected in the brass case. “You’ve stamped my initials on the front. And it’s ticking again!” she exclaimed, putting it up to her ear. A broad smile burst across her face. She pressed the crown switch and the case flew open to reveal a second-hand sweeping round the clock face above the slower minute- and hour-hands.

“There’s something else,” Robert said.

Taking the watch from her, he twisted the crown three times. A fourth hand appeared from behind the hour hand and swirled around the watch. He stopped it over the minute hand, and the watch chimed loud as a bell.

“I added an alarm,” he explained. “I thought it might come in useful.”

“I bet you had to rejig the entire workings to get it to do that,” Lily said.

“Not the entire workings, just a few cogs and levers here and there. I learned a lot of it from your pa’s teaching: he’s been showing me how to move mechanical workings about to change the way a thing functions.”

“Well, it’s the best present ever.” Lily looked so proud of him.

“What about my gift?” Malkin asked haughtily.

“That was good too, but this is even better. Thank you.” She kissed Malkin on the snout and Robert on the cheek.

“It’s a pleasure,” Robert mumbled, fiddling with his cufflinks as a wave of heat flushed through him. “Now you have all the time in the world.”

Lily laughed. “And I shall keep it always. In my pocket.”

“We ought to go downstairs and join the party,” Malkin suggested.

“Perhaps.”

Lily picked up her book and stepped towards the door. Then she stopped and turned mischievously towards the telescope and the east window. “I thought we might only stay at the party for a little bit – there’s somewhere else I wanted to go.”

“Where’s that?” Robert asked.

“Take a look.” She tilted the telescope towards him.

Robert bent down and squinted through the eyepiece. The twilight countryside was swathed in patches of fog, thick as fallen clouds. “What am I looking for?” he asked Lily.

“Beyond the last house on the left, in the meadow by the bend in the river, at the far end of the village.” Lily pointed for him and, through a gap in the mist, Robert spotted it…

A red-and-white striped hot-air balloon and ship-shaped wooden gondola, tethered beside an enormous Big Top that had been erected inside a high white wooden fence. The balloon’s silks flickered like an oil lamp, illuminating a long queue of excited-looking villagers running all the way down from the lane at the edge of the field to the kiosk and spiked gate set into the high fence around the circus.

“Let me look! I can’t see a thing!” Malkin bounced about at Lily’s feet and scraped at Robert’s leg.

“Foxes don’t do telescopes.” Robert shifted his focus to the sign above the entrance way. “Slimwood’s Stupendous Skycircus,” he read.

“That’s where we’re going.”

Lily handed him the birthday card.

“It’s a queer poem,” he said at last, when he’d read it. “What does it mean? And what are the two clues?”

“This is the first one.” Lily showed him the ticket.

Robert was dumbfounded by the drawing of the winged girl and the message. “And the second?” he asked.

“This.” Lily pulled the red notebook from behind her back. “It belonged to my mama. It’s about a project of hers to design mechanical wings,” she explained as Robert flipped through pages of amazing drawings and sketches of winged figures.

“You’ve no idea who sent these?” Malkin asked.

“Maybe this winged girl, Angelique. She’s asked to see us. I think she might be a hybrid too, like me. She looks nice.”

“I’m not sure, Lily. How would she have got hold of your ma’s notebook?” Robert tapped the red cover. Something about the notebook’s sudden and unexpected appearance made his head itch with worry. “It could be a trap. Why else would whoever had this book send it to you, rather than to your father?”

“Because it’s my birthday.” Lily snatched the notebook back and shut it with a snap.

“But how would they know that?” He handed her back the ticket and card as well. “Don’t you think it’s odd for a circus to come to Brackenbridge? There’s not been one before. Such grand shows never normally visit such tiny villages.”

Malkin stuck his tongue out of the side of his mouth. “Robert has a point,” he said. “For them to arrive on your birthday, of all days…then there’s these clues and presents, and the invite… I mean, what on clunking earth…?”

“Oh, I don’t know, Malkin – that’s why we should go and find out.” Lily looked at the pocket watch. “It’s almost six twenty now. We can probably arrive at the circus before it starts at seven thirty. See the show, meet Angelique and be back by nine, before the party’s even halfway over.”

“We can’t just disappear without speaking to any of the guests.” The fox wrinkled his nose disapprovingly. “Your father’s expecting you to put in an appearance.”

“Then we shall greet everyone briefly, before we sneak off,” said Lily. “What do you think, Robert?”

Robert wasn’t certain they should be going at all. He wondered if he should mention the fact that Lily’s da was planning a surprise speech and present-giving at nine? But then he remembered he’d promised to keep that a secret. Did such promises apply if you were running off to see the circus? He thought he’d best keep his mouth shut just in case they did. If it looked like they weren’t going to be back in time, he might mention it to Lily then – to be sure she’d get a wriggle on.

Besides, he did love a puzzle, and this one was very intriguing. The circus could be fun and this might be his only chance to see it…

“Fine,” he said at last. “Let’s do it.”

“But if we get into trouble,” Malkin added, “it was your plan.”

Lily ruffled his ears. “We won’t get into trouble. When have we ever got into trouble?”

The fox sighed deeply. “I’m not going to even dignify that with a response.”

Lily picked up the ticket, card and notebook. She was glad she had a new mystery to solve. At last she felt as if she was doing something exciting and worthwhile on her birthday.

“Don’t worry so much, both of you,” she said, shutting the window. “We’ll be back before Papa’s even missed us.”