‘It’s not a matter of fair,’ Isaac said. ‘I am a Reader. So are you. You don’t get to choose, any more than you get to choose to be a fish instead of a person.’

Geryon gave me a choice. Not much of a choice, really, but at least he’d offered. Alice didn’t say it, though, partly because she didn’t want to argue but mostly because Isaac had stopped short, staring down at the map in his hands.

‘This is the edge,’ he said. ‘Now what?’

‘Is there something on the other side?’ Alice suggested.

Isaac turned the map over, but the other side of the parchment was blank. He held it up to his glow-wisp, trying to see through it, then shrugged and handed it to Alice. She looked at the creased rectangle and thought for a moment.

Unfolding it got it to work the first time. So maybe . . .

She tried creasing it back up again the way it had been, but it only flopped open. Then she bent it the other way, folding the section of the map they’d already passed through underneath the section they were standing in. At once she felt something happen. The page twitched under her fingers. With mounting excitement, she ran her hand around the edge and found that it would open in a new direction, at right angles to the first. She unfolded another section with that faintly sticky sensation to reveal the continuation of the path.

She held it up for Isaac to see, unable to help a triumphant smile, and he grinned back.

‘Brilliant,’ he said, and Alice found her cheeks unaccountably flushed.

She held the map out in front of them, orienting herself, and led the way into the depths of the library.

Before they reached the end of the second square of map, the library started to change. Shelves appeared at odd angles to the rest, forming squares or triangles facing inwards or outwards. The pathways started to curve, then lost themselves altogether and became only the spaces between shapes and clusters. At the same time, the books themselves started to thin out, until each bookcase bore only a couple of lonely-looking volumes or none at all.

It was the place Alice remembered from her first night in the library, what Ashes had referred to as Geryon’s back rooms. Seeing it again made her a little nervous, and she found herself tracing the scar on her cheek with one finger. Isaac seemed perfectly comfortable, though, and she was determined not to show any hesitation in front of him. She kept her eyes on the map and her feet moving forward.