‘Ashes,’ Alice said, in a tone of extremely strained patience. ‘Where are we?’

He sighed, which was an odd sound to hear from a cat. ‘We’re inside the book, of course. The one you Read. The Swarm.’

Alice laughed. ‘You’re not serious.’

‘Don’t ask questions if you don’t want to hear the answers,’ Ashes said. He swished his tail, offended, and started off down one of the corridors. Alice, feeling the first thrills of fear, hurried after him.

‘All right, all right,’ she said. ‘We’re inside the book. How did we get here?’

‘You brought us,’ the cat says. ‘You have the gift, apparently. You’re a Reader.’

‘I’ve read a lot of books,’ Alice said, ‘and nothing like this has ever happened.’

Ashes sniffed. ‘It doesn’t work with just any book, obviously. This is one of Geryon’s. It’s special. This particular kind of volume is called a prison-book, because it’s what Readers use to lock up all sorts of nastiness.’

‘Nastiness?’ Alice looked over her shoulder, but saw only darkness. ‘There’s something in here with us, you mean?’

‘Of course. The Swarm, presumably.’

‘What’s that?’

‘How should I know?’ Ashes said. His voice was strained. ‘I just know that if Geryon shoved it in a prison-book, it probably isn’t friendly!’

Alice thought about that for a moment. The corridor they were following bent slowly to the right, so that their original room quickly passed out of view. More strips of moss glowed on the walls, and here and there iron fittings of no obvious purpose were hammered between the bricks, weeping long, rusty stains.

‘So,’ Alice said eventually, ‘how do we get out?’

‘I thought you’d get around to that,’ Ashes said. ‘There are at least two ways out of a prison-book. Another Reader on the outside can pop you out again, if he knows the book well enough.’

‘Could Isaac do that?’

‘Maybe with a year’s study,’ Ashes said. ‘And a good deal more power than he’s got.’

‘What’s the other way?’

‘You find the prisoner,’ Ashes said, ‘and kill it.’

‘Excuse me?’

‘It’s the way the prison-books are written,’ Ashes said. ‘The Reader goes into the prison-book, conquers the prisoner, and the book lets him out. Or her out, in this case.’

‘But,’ Alice said, ‘I don’t want to kill anything.’

‘Unless the Swarm is something you can argue to death, I doubt it’s going to matter. The Reader is supposed to be prepared for this kind of thing, with magic fire and silver swords and so forth. Normally you don’t just wander into a prison-book in your nightshirt and carpet slippers.’

‘I haven’t even got carpet slippers,’ Alice reminded him. The bricks underfoot were worn with years and slimy with damp, but the occasional sharp corner still scraped painfully against her bare feet. ‘So what are we going to do?’