Alice pulled herself together and marched forward. If she could see his lantern, he could probably see hers, so there was no point in trying to be sneaky. She raised the hurricane lamp over her head and called out.

‘Isaac! It’s you, isn’t it? I know you’re there!’

She rounded a bank of shelves and found herself at the low table Mr Wurms usually used. The scholar was nowhere to be seen, but another lantern was sitting on the table. Behind it, rising slowly from a crouch, was Isaac. He was still in his dirty, tattered coat, and his hair was limp and heavy with sweat. He had crude bandages around both his hands and halfway up one arm, and Alice could see spots of blood already soaking through the linen.

‘Alice?’ he said, and all the tension went out of him in one breath. ‘Oh, God. Of course.’ Isaac flopped down onto one of the benches beside the table. ‘I thought I’d had it when I saw someone coming after me.’

‘You,’ Alice said. She didn’t know what to think. Half a dozen things to say crowded towards her tongue, but the one that finally escaped was, ‘How did you get out?’

‘Geryon puts too much faith in his guard dogs.’ He sounded a little smug.

‘You lied to me about the Siren.’

‘Oh.’ Isaac had the decency to look a little bit embarrassed. ‘I didn’t lie, exactly. I just didn’t mention this.’

He dug in his pocket and produced a small piece of jewellery, a red stone in a silver setting, like a brooch or a necklace. The stone was dull and plain, and a wide crack ran most of its length.

‘It’s a sort of . . . battery,’ he explained. ‘My master gave it to me. It let me feed enough power to the Siren that it caught even Geryon off-guard. But it only works once, and I knew I’d need it—’

He stopped, looking puzzled at Alice’s expression.

‘You’d need it to escape,’ Alice said. ‘Because you’re a thief.’

‘You don’t need to say it like that. It’s nothing personal. The book is just something my master wanted, so he sent me to get it.’ He shook his head. ‘Anyway, Geryon didn’t even know where the Dragon was. I can hardly be stealing it from him if he didn’t know he had it, can I?’

‘We were supposed to get it back for Ending,’ Alice said. She didn’t mention her own goal of using the book to trap Vespidian.

‘Ending told me we could make a deal for the book,’ Isaac said. ‘My master wants the book, and he’d be willing to bargain generously for her help in getting it. But she betrayed us, Alice. No one could have led Geryon to us except for her!’

‘She didn’t have a choice,’ Alice said.