The groups of shelves they walked by started to change. She passed one cluster that exuded frigid gusts of air tinged with the smell of new-fallen snow, and another that gave off a rumble like distant thunder and had the metallic tang of ozone. Flickering lights within one octagonal ring played green and purple against the ceiling. An enormous triangle smelled of new-mown grass, and from within an oval she could hear the faint cheering of multitudes and the ring of steel on steel. A pentagon leaked a sullen red glow and the vile stench of brimstone.

When they reached the edge of the map again, she showed Isaac how to fold it and open it again. This time, the green line didn’t continue off the end of the page, but led to small dot in the centre of a hexagonal ring of shelves some distance ahead of them.

‘That must be it,’ Isaac said. ‘That’s where the book is hidden.’

Alice nodded, oriented herself from the map, and pointed the way. They passed a rectangular set of shelves that leaked steam from every gap, from which Alice could hear the squeal of squeaky bearings and the low thump of an engine. She longed for a little peek at what was inside – how could just a peek hurt? – but Isaac pressed onward.

This is all probably old hat to him, I suppose. Alice tried to imagine growing up with all this, with magic in every corner and the knowledge that you were different from everyone else.

‘Alice,’ Isaac said, after a long silence. There was a hint of nervousness in his voice. ‘Did Ending tell you anything about what we would have to do to retrieve this book?’

‘Only that it was lost.’ Alice thought back. ‘And that it was guarded. If it’s called the Dragon, does that mean there’ll be a dragon guarding it?’

‘No,’ Isaac said quickly. ‘That means there’s a dragon inside the book. Whatever guards it will be on the outside.’

‘Whatever it is, it must be something awful,’ Alice said, ‘since Ending thought it would take both of us to get past it.’

‘That makes sense.’ Isaac sounded as though he wished it didn’t. ‘Those little . . . things of yours—’

‘I call them swarmers.’

‘Right. Can they fight, do you think?’

‘I haven’t tried,’ Alice said. ‘Except for poking Mr Black in the ankle.’

‘Have you tried using them internally?’

She shook her head. ‘Geryon mentioned that, but I don’t really know what it means.’

‘If you pull the creature into yourself, rather than out into the world, you can take on some aspect of it. Even turn yourself into it entirely, if you’re good enough.’

Turn myself into a swarmer? Alice was dubious. It wouldn’t be big enough. Where would the rest of me go?