Lily, Robert and Malkin crept down the grand staircase to the front parlour, where a gaggle of guests were milling around, talking before dinner.

Lily glanced about the crowd, searching for Papa, and though she couldn’t see him anywhere, she recognized a few faces in the room.

There was the mayor of Brackenbridge, talking to the parson of nearby Brocklebridge Church and Mr Chantry from the second-hand bookshop. There was Inspector Fisk from Scotland Yard, who’d helped Robert, Lily, Malkin and Tolly foil a plot by Robert’s grandfather, the infamous escapologist Jack Door, to steal the Queen’s diamond. He was talking with Papa’s lawyer, Mr Rent, who’d been a partner in a firm called Rent and Sunder, before Mr Sunder had run off with their old housekeeper Madame Verdigris and a ton of Papa’s patents and papers, never to be seen again.

And there was Mrs Chivers, whose clockwork canary Robert had once repaired. It was sitting on her shoulder now, chirping incessantly.

The rest of the room appeared to be filled with mechanists and professors from the guild. Lily noticed that there were no ladies among them, and remembered that, on the first page of her notebook, Mama had mentioned how hard it was for female scholars to become mechanists.

There’d certainly been no talk of such career opportunities at Miss Scrimshaw’s Academy – the awful finishing school Papa had attempted to press-gang Lily through last year. The life of a young lady, according to that place, was meant to be an endless parade of polite tea parties, cluttered with doilies and bone china, or else a stream of embroidery, etiquette and deportment classes. If Mama had truly altered things and gone against the grain of those ideas, why was it no one else had followed her example?

Anna was the only other woman Lily knew who took exception to those kinds of rules. She looked for her among the throng of guests, and Tolly too. She was sure Robert had mentioned they’d been invited, but she couldn’t see them anywhere. She wanted to at least speak with Anna before they snuck off, and perhaps she could persuade Tolly to accompany them to the circus – they did have four tickets, after all.

Finally, she spotted the stout figure of Anna in the far corner. The journalist and aeronaut looked rather incongruous, for, unlike the rest of the guests who were in evening dress, she was wearing her best bloomers and leather flying jacket. Although, in a concession to the formality of the occasion, she had taken off her hat and goggles, and had pinned her hair up in a neat plait around the top of her head.

Lily wanted to ask her where Tolly had got to, and maybe tell her about the card, ticket and red notebook, but as she approached she saw that Anna was deep in conversation with someone – a tall professor, with bulbous ears and a bald patch. The professor had his back turned to her, and so did Anna, but their discussion was so interesting that Lily couldn’t help but eavesdrop.

“I’m writing a piece on hybrids,” Anna was saying, “and I need some facts and figures for my article. I hear you worked at the Mechanists’ Guild for a time so I wondered if you might be able to help… How many hybrids are there in England, would you say?”

The tall professor laughed and took a swig of champagne from the long-stemmed glass in his hand. “A good question, Miss Quinn. But, honestly, I’ve no idea. They’re not my speciality. If I had to make a guess, I’d estimate probably only half a dozen or so. The hybrids that were created were…experiments. Many of the early incarnations did not survive more than a few years, and those that did aren’t seen by the world at large… For obvious reasons – I mean, the sight of them is frankly unacceptable.” The professor gave an involuntary shudder. “But, fortunately, such work is no longer being undertaken. The only mechanist I know who dealt in such things – apart from our poor deceased colleague Professor Silverfish – was a Dr…Droz, I think the name was. A thoroughly unpleasant and discredited character.” He leaned in closer to Anna, and whispered theatrically, his eyebrows wiggling like hairy white caterpillars, emphasizing each word. “Thrown out of the guild years ago. Though the details of that are not for me to divulge.”

Lily was about to interrupt him when he continued; “Legend has it that Hartman and his wife were involved in hybrid research too, you know! The gossip was of some corrupted creature with a clockwork heart.”

Lily felt a horrible shiver of panic.

“Of course, we at the guild disavow hybrid study entirely,” the professor continued.

“Why?” Anna asked.

He shrugged. “Turning humans into hybrids is unethical, it changes who they are. Creating mechanicals is a different thing. But creating hybrids – half-and-halfs – it’s against the laws of nature. It contaminates us. People should be left as they are. I mean, why meddle with what the great maker himself intended?”

Anna put her empty glass down on a side table. “Even if helping them means they’re happier and healthier?” she asked. “Even if it saves someone’s life?”

“Especially if it saves someone’s life,” the professor said. “If you change someone with clockwork, turn them into a hybrid, how are you saving them? Would you want them to have to deal with that stigma? It’s worse than being a mechanical. No, better they remain normal and a little damaged: a pure human who meets their fate with dignity, rather than a transformed freak.”

Lily gasped and felt the air knocked out of her. Did people really believe such things? Her blood boiled just to hear his little speech. He knew nothing of hybrids – if it wasn’t for her clockwork heart, she wouldn’t even be here, alive, on her birthday. She was no freak! Why did he think he had the authority to spout such vile opinions, the oaf!

“How could you possibly understand what it feels like to be a hybrid?” she asked, stepping between him and Anna and thrusting herself into their conversation. “Who are you to say what’s good or bad?”

The professor’s eyes widened in alarm. He was obviously rather surprised to be interrupted in full flow. “My dear young lady, it’s common knowledge that hybrids are problematic, which is why we at the guild banned their creation.”

“Lily!” Anna cried. “It’s so good to see you.” She kissed Lily on both cheeks.

“And you,” Lily replied. But she was still fuming about the professor’s remarks.

“Do you know each other?” Anna asked.

Lily shook her head.

Anna introduced them. “This is Professor Manceplain – a noted expert on mechanical studies. Professor, this is Miss Lily Hartman, John’s daughter.”

“A pleasure, young lady.”

Lily shrugged. It was certainly no pleasure for her to meet such a horrible man. For a moment there was an awkward silence, of the kind grown-ups sometimes fall into at parties when nobody knows what to say.

“I’m so glad you’re here, Lily,” Anna said at last. “Your father told me it was your birthday, and we’ve a present for you. Only I left it with Tolly, and I can’t seem to see him anywhere… Perhaps we should go find him?”

She took Lily’s arm and led her away from the tall professor, the pair of them pushing through the sea of bodies.

“How could that man hold such idiotic views?” Lily asked. “Why were you talking to him? Are you investigating something to do with hybrids?”

“Thank goodness you came over,” Anna said, not answering any of her questions. “The conversation was getting onto rather shaky ground. I don’t know what I would’ve said if it had continued! But I really need to speak with your father,” she went on, spotting him and pointing him out. “Why don’t you find Tolly? He’s got your gift, and we can catch up later…” And she vanished into the crowd.

Someone tapped Lily’s shoulder. It was Robert. “You’ll be pleased to know I’ve seen Tolly,” he said. “He’s hiding in the kitchen.”

The sideboard downstairs was laid out with Mrs Rust’s various replaceable tool-hands. Pre-prepared dishes lined the table, awaiting their delivery to the dining room. There was a large boiled salmon with cucumber and lobster cream perched in a grand blue-and-white serving dish, alongside veal croquettes and a leg of lamb on a bed of blanched spinach and roasted potatoes. Then for pudding there was a gooseberry tart with whipped cream and orange jelly and a lemon cake. And cheese and biscuits. It all smelled amazing and it felt almost a shame to go out and miss such a feast.

Tolly sat alone among the platters of food, his chair turned towards the hearth. His tanned face with its thatch of chestnut curls looked sad, but then he glanced up and saw Lily and pasted on a smile. “Happy birthday, Lil! Hello, Robert! Are you having a good party?”

“It’s not really her birthday party,” Malkin said. “More a stuffy event for mechanists.”

“That’s why we stepped out,” Robert explained.

“Too right!” Tolly leaned back in his chair. “I didn’t fit in there neither. It’s full of blimmin’ professors – the crème de menthe of the mechanist community, supposedly. Anna was talking to some awful fella about her article, so I decided I’d come in here and sit by the fire on me own for a bit.” Tolly leaned forward in his chair and straightened his jacket. “Oh, I almost forgot, Lil. Me and Anna brought you a gift.”

He felt about in his pockets and pulled out a leather wallet. When Lily opened it, she discovered it was full of tiny implements – miniature lock picks, each one barely longer than a match.

“We thought they’d come in handy on your adventures,” Tolly explained. “Might have better luck with them than hairpins.”

“Thank you.” Lily laughed. “It’s truly what I’ve always wanted.” And it was.

“I brought some firecrackers an’ all,” Tolly said, pulling a handful from his pocket to show them. “Just to liven things up,” he explained. “But I don’t think it’s that kind of a do.”

“No, it doesn’t seem to be,” Lily said sadly. Then she perked up. “I know something that might cheer you up, Tolly. And it’s far more fun than this dull party.”

“Oh, what’s that?”

Lily and Robert showed Tolly Mama’s red notebook and explained how it had arrived with the bizarre birthday card and circus invite. Tolly flicked through the book as they told the tale, taking in all the wonderful drawings and illustrations of flying creatures.

“It’s a proper mystery,” he said when they finally finished. “Just how did Angelique and the rest of these circus folk get hold of your ma’s notebook in the first place?” He handed it back to Lily.

“That’s what we intend to find out,” Robert said.

“As well as catching the show,” Malkin added. “I’m hoping there’ll be fire-eating, juggling and some hummable tunes. But obviously no mimes – they’re the worst.”

Lily put the book away and checked her pocket watch. “It’s seven now,” she said. “We should probably get going. Why not come with us?”

“Spit and sawdust!” Mrs Rust said as she bustled in to pick up trays of food. “Did my metal ears deceive me? Are you off out?”

“We thought Tolly might like to take a turn around the garden, Rusty,” Lily said. “He hasn’t seen it before.”

“Dough-hooks and dishcloths! What the tock for? It’ll be dark out.”

“A bit of fresh air. He’s feeling a little peaky, actually.”

“I am?” Tolly looked confused. Then, when he saw the frown on Lily’s face, he clutched his stomach and played along. “Ooh, yes, I’m afraid I am.”

Mrs Rust gave a loud tut. “Well, wear a coat.”

“Of course, Missus.” Tolly clasped Robert’s arm and hobbled towards the cloakroom that led to the back door.

“And, Lily,” Mrs Rust added, “before you go wandering off—”

“We aren’t!”

“I know you better than that.” Mrs Rust put down her tray. “Make sure you’ve a scarf. It’s cold out. In fact, I wasn’t going to give you this till later, but it seems as if you could use it now.”

She opened a drawer in the kitchen dresser and took out a rather rumpled-looking package. “Steam-fountains and stockpots! It’s got a bit squashed.” Mrs Rust placed the package in front of Lily on the scrubbed table. “That’s from us mechanicals, my tiger.” She gave a wheezy cough. “Well, that is to say, mostly it’s from me, as I’m the one who made it.”

Lily’s heart soared. From a day when it seemed everyone had forgotten her, she’d ended up with a whole armful of presents.

She kissed Rusty on her dented metal cheek and set to opening the package. Inside was an orange-and-black striped scarf. The longest scarf she’d ever seen. She wound it round her neck, but even after she had done so a number of times, the end still trailed on the floor.

“It’s lovely,” Lily told Mrs Rust. “If a spot on the large side.”

“Fulcrums and fenders! Sorry about that,” Mrs Rust said. “I’m not the best at knitting. Thing is, I can cast on, but I’ve not quite fathomed how to finish. So I keeps going until the wool runs out. Never mind, I’m sure you’ll grow into it.”

“If she turns out to be a giraffe,” said Malkin, who’d returned from the cloakroom.

“Maybe I will, Malkin.” Lily hitched up the end of the scarf and stuffed it into the pocket of her dress. To Mrs Rust she said, “Thank you, Rusty, I shall treasure it for ever, and never take it off, not even indoors!”

Mrs Rust gave a bolt-filled grin. “Gridirons and girders! I should think not! You be careful out there, don’t step on any of Springer’s begonias, and mind you’re back in time for your father’s big speech at nine!”

In the cloakroom the back door was open, spilling out heat and letting in the dark and a chilly breeze. Just beyond the last rectangle of light, Malkin and the others stood on the bottom step in the gathering fog, waiting for her.

Lily took her coat from the rack and thrust her gifts into its pockets, glancing back into the kitchen as she did so.

Mrs Rust stood framed in the doorway, bent over a tray that she was filling with food. Lily’s stomach rumbled. She felt suddenly famished. She wondered if she should go back and steal a croquette or two for later, but then realized they’d only get squashed in her pockets. Anyway, there was sure to be plenty of leftovers when they returned.

She was glad to be leaving the party. She hoped by the time the four of them got back that dinner would be over and all those stuffy professors would’ve retired to the smoking room or, better still, gone home. Papa probably wouldn’t even notice they were missing.

In the meantime, she’d had enough of duty for one evening. It was time for her birthday treat…and to get some serious investigating done! They were off to see the circus!