Lily, Tolly and Malkin rode from the theatre with Anna and Constable Jenkins in the back of the police wagon. It turned out Anna had arrived a few minutes after the show had started and found the theatre doors locked. When she couldn’t get in, she’d tried to break them down, but she wasn’t strong enough on her own.

Then, she told them, she’d heard some kind of ruckus, and a great crowd of people had smashed their way out from the inside, pouring into the daylight and dispersing almost at once. She’d tried to find her friends amongst them, but they weren’t there, and it had been another few heartstopping minutes before they finally emerged with Constable Jenkins…and without Robert.

Lily listened distractedly to this story and stared out at the sunny streets of London. Decked in their bright Jubilee bunting, they were at odds with the sombre mood inside the cab. She couldn’t quite believe the darkness they’d encountered at the theatre. If someone had told her that morning she would be part of such an unnerving turn of events, she could not have imagined it.

Things hadn’t become any less scary after the Doors disappeared. The inspector had turned red-faced with anger, and started kicking at the spirit cabinet, searching for the secret door. The rest of his men had swarmed the theatre, shining lamps into odd corners of the stage and pouncing on the final few confused members of the audience trying to leave.

Lily, Tolly and Malkin had stood shocked in the centre of the stage, ignored by everyone. Finally Constable Jenkins had offered to take them back to the guild in the police wagon.

Lily shifted agitatedly in her seat. Anna put an arm round her, but soon they arrived at The Daily Cog and it was time for her to get out.

“If you need anything,” Anna said, “anything at all, we’ll be here waiting, both of us. I hope they find Robert and his ma and sister, Lily. And I hope you get back to your papa safely. Send him good wishes from me, and tell him I’ll do everything within my power to help. But in the meantime we’ll keep looking into your riddle.”

“What riddle?” the constable asked as Lily waved Anna and Tolly goodbye.

She ignored him. As the police steam-wagon pulled away, she and Malkin watched their friends disappear around the side of the Daily Cog building. Suddenly Lily felt quite upset. “Why didn’t you tell us you were setting a trap for Jack?” she demanded of Constable Jenkins.

“The same reason you didn’t tell us that you’d found the locket,” he replied. “We didn’t want you getting involved.”

“Didn’t Robert deserve to see his ma?”

“We would’ve put them in touch after our undercover operation was over.”

“Seems to me you’ve made a right mess of things,” Malkin admonished the constable.

Lily was inclined to agree. The police had failed to capture Jack or Selena, and she’d lost Robert, after she’d made a promise to look after him.

“I’m sorry,” Constable Jenkins said, apologizing to Lily rather than the fox. “You should’ve trusted us. And we you. We can only try and make amends. You’d better tell me everything you know about the Moonlocket. And the riddle Miss Quinn mentioned, whatever it is. It may be our only clue to finding Robert and the Doors again.”

So Lily described the map and the two mysterious code words she and Robert had translated: flows underground.

The constable wrote them down in his notebook.

“They’re the end part of a sentence,” she explained. “I caught a glimpse of the rest of it on the other half of the locket when Selena had it. Something-something-something, flows underground. Do you know what it means?”

Constable Jenkins shook his head. “Not yet,” he said. “It’s a strange one, I’ll grant you that, but I’m sure we’ll solve it.”

Lily wondered when that would be. Soon, she hoped. Jack was a criminal on the run, willing to do whatever it took to find the Blood Moon Diamond. For Robert and his ma and sister, those kinds of odds weren’t good.

The police wagon jerked to a stop outside the Mechanists’ Guild. As she and Malkin jumped down from the passenger compartment to join Constable Jenkins on the pavement, Lily tried to shake the horrible feeling that everything was lost.

Constable Jenkins paused outside the guild workshop, letting Malkin and Lily enter first. There was Lily’s papa, standing before the Elephanta. He turned to stare at her, his hands clasped behind his back. It was a posture he only adopted when he was exceedingly cross. Beside him was Captain Springer, his arms tight across his chest, bow legs jittering.

Lily averted her eyes from them. She felt guilty that she had run away from home, and then the guild too, and got into so much trouble. She was about to explain to Papa what had happened when he rushed forward and hugged her to his skinny frame. “Lily,” he cried. “Where’ve you been? And where’s Robert? We were so worried about you both. I’d no idea what’s been going on.”

Constable Jenkins coughed, awkwardly. Papa spotted him and then Malkin, hiding behind his legs. “Malkin, you moth-eaten mongrel!” he cried. “You were supposed to look after Lily and Robert! Keep them out of trouble.”

“I did my best,” Malkin muttered.

“What happened?” Papa asked the constable.

“Your daughter and Robert decided to visit The Theatre of Curiosities,” the Constable explained. “To make contact with Robert’s mother, Selena, and his sister Caddy. Unfortunately they then interrupted a rather delicate sting operation, and, I’m afraid, Sir, Robert and his entire family were taken by Jack Door.”

“Taken where?”

“At this time, we don’t know.” The constable sounded rather embarassed. “But we’re working on it.”

“They all just disappeared,” Lily said. “In a puff of smoke.”

“Good grief!” Papa adjusted his half-moon glasses, which had become skewed on the bridge of his nose. “I told them both to stay at home…” he admitted to Constable Jenkins.

“So did we, Sir,” the constable advised.

Papa’s hands shook against Lily’s back. “I wish I’d left someone sensible to keep an eye on them. After the telegram from Mrs Rust I was distraught with worry…then I didn’t hear a thing… But whatever kind of trouble Robert was in, he would’ve been safe at the manor, surely? At least, that’s what I thought. It was in such a state yesterday, when I got there…” He trailed off, hugging Lily closer to him and gazing distractedly around the room.

Lily pushed free from his grasp. “We weren’t safe at home, Papa. We found Jack at the shop and then he came looking for us. All we could think to do was to try and find Selena, and then come and see you. But you’d gone. And now that you’re back, we need to look for Robert at once.”

Papa seemed to come round then. “Best leave everything to the police, Lily.” He looked to Constable Jenkins.

“That’s right,” Constable Jenkins said. “This whole situation is far too dangerous for you to be involved in, Miss. We can deal with things now. You should probably just stay here and get some rest.”

“What about Robert?” Lily said. “I have to find him. I made a promise to help.”

“No, Lily,” Papa said. “With this Jack Door…anything could happen—”

“I’m not at risk from him, Papa; Jack let me go.” She turned and appealed to the constable. “I know Robert best. I’m the one who understands him. Robert and I, we’ve been investigating the Doors for days, I’ve got as much of a clue about them as anyone.”

“I don’t think so, Miss… Besides, London’s too big. The Doors and your friend could be anywhere. Best leave it with us – we’ll lay hands on them soon enough.”

“Listen to him, Lily.” Papa gripped her arm. “He’s right. I’m responsible for your safety. Remember what we talked about at home, before I left? You’ve a good heart, but I can’t let you get involved in this any more. If anyone should be out there searching for Robert, it should be me.” He smiled at the constable. “Thank you for bringing her back, Sir. I’ll see that she stays out of trouble. Now, if you wait down here, I shall come to join the search with you when I return.”

Lily, Papa and Malkin climbed the stairs of the guild’s accommodation wing, then walked past the frozen automatons she and Robert had noticed last night. To Lily that already seemed a lifetime ago.

“But we do have a clue,” Lily said suddenly.

“What’s that?” Papa asked.

“You said we didn’t have a clue, but we do: flows underground. The words Robert and I translated from the locket. They have something to do with where the diamond’s hidden.”

“And you told the constable this?” Papa asked.

She nodded.

“Well then, he’ll probably be able to work out what that means.” Papa unlocked the door to his quarters. “Why don’t you take it easy for a bit?” he said, escorting her and Malkin in. “You’ve had a strenuous couple of days. I’ll get one of the mechanicals to bring you up some food later this evening. A plate of something soothing. Plus, I brought a case from home, for you and Robert.” Papa indicated a travel trunk among the others in the centre of the room that hadn’t been there last night. “By the time you’ve changed into some fresh clothes, had some dinner and a nap, I’m sure the police will have solved everything, and Robert will be back with us.”

“It’s not even dark,” Lily said as she watched him step around the camp bed and draw the curtains to block out the afternoon light.

The truth was, she did feel rather tired. She wondered if a rest was actually a good idea.

“It’s better this way,” Papa said as he closed the door. “Try to sleep for a bit. I’ll let you know at once if there’s news.”

After he was gone, Lily took Mama’s ammonite from her pocket and placed it on the bedside table. Then she lay down on the bed.

Papa was right, she did need to rest briefly. Later, when her mind was clear, she would be far more capable of helping Robert. And hopefully, by then, the police or Anna or even Papa would have discovered something new. Malkin nuzzled her ear and she rubbed woozily at her face and put her head on the pillow, shutting her eyes for a brief moment…

Flows underground.

The phrase jolted her awake, tumbling around inside her head like the locket twisting on its chain. If only she could figure out what it meant.

Blearily, she reached over and wound Malkin with the winder key on the chain around his neck. Then she got up and went to the window, throwing back the curtains.

The room was on the top floor of the guild and she could see the whole of the city. Behind the spire of St Paul’s Cathedral the sun was setting, bathing everything in a bright orange light. She must’ve slept for a good few hours. Was it really only last night she and Robert had stood here waiting for the clouds to pass, so they might see the moon and stars? She’d thought that all clouds would pass with time…but maybe she was wrong.

Robert was lost somewhere out there with Selena and Caddy. She gave a deep sigh.

“What are we to do, Malkin?” she cried. “It feels like time is running out.”

She put her head in her hands and thought about how angry Jack was, and how hotheaded he’d been about the locket. “Maybe I’m wrong. Maybe Jack will let Robert go? He got what he wanted. And they are family.”

Malkin jumped up on the window ledge beside her, and licked her face. “I don’t think so, Lily. Jack doesn’t seem the sort to forgive a grudge. But don’t you worry,” he said, “we’ll find Robert. I’m sure of it. We’ll leave and look for him as soon as it’s light. Perhaps Tolly will assist us? He’s a good sort. Seems to know London.”

Lily nodded. She’d been wondering about Tolly. Scraping around alone on the streets gave him a kind of freedom. She remembered the joyful feeling of walking with him yesterday morning, how he knew every landmark. He’d even told her about…

“Of course!” she shouted. “Malkin, it’s the Fleet River that flows underground.”

“What?” Malkin said.

“The map on the locket showing where the diamond’s hidden, it’s of the Fleet River. Tolly told me it ran underground through the sewers, right beneath Queen’s Crescent, where the Doors used to live.”

“You think Jack will have worked that out?”

“Robert will – he has to!” Lily said. “And Jack will want to get the diamond as soon as possible, so they’ll probably go there straight away.”

“Then we should tell someone right now.” Malkin jumped down from the window ledge.

“Good idea,” Lily said. “We’ll go back to Anna. She’ll know what to do.” She ran to the door and tried the handle, but it wouldn’t turn. And with shock she realized that Papa had locked them in.