Alice found herself on a grassy hill, overlooking a little valley with a stream that splashed and burbled through a racecourse of mossy rocks. She could see for miles in all directions, across rolling grassland spotted with small forests. Mountains, blued with distance, lined every horizon, as though she were standing at the bottom of an enormous basin. The air smelled sweet with growing things, and a warm sun beamed down from overhead.

Long green-and-yellow grass stalks rustled all around her, reaching up under her dress to brush against her thighs. She brushed them away, wishing idly that she’d worn trousers, and turned in a careful circle. Not far away, on the highest point of the hill, there was an enormous willow tree so perfectly circular, it resembled an overturned bowl.

That had to be where she was intended to go. Alice felt a brief, rebellious spark, and wondered what would happen if she turned her back on it, just walked out across the beckoning fields and never went anywhere near the tree. But Geryon was watching, and in any event he’d told her that the world of a prison-book wasn’t really real, only real enough to contain the prisoner. She wondered if she’d eventually walk into a painted backdrop, like an incautious actor on a film set.

Reaching out for the silver thread that led to the Swarm and keeping it firmly in her mental grip, Alice walked towards the tree.

She reached the curtain of hanging leaves, and parted it with one hand. The inside was shadowy and quiet. The willow’s overhang had smothered the grass, leaving bare, hard earth underfoot, broken here and there by the knots and gnarls of the great tree’s branches. Overhead, the branches of the trees stretched in all directions.

On one of those branches sat a . . . thing. When Geryon had said ‘tree-sprite’, Alice had pictured something that looked like Vespidian, only painted in delicate greens and browns instead of yellow and black. This was a different sort of being altogether, vaguely ape-like in shape and massively bulky, covered all over in thick, dry bark. It had no head, only a slight bulge above its shoulders that showed two deep-set eyes. Enormous, outsized arms ended in heavy, gnarled fingers tipped with ragged claws, and short but similarly massive legs sported long, finger-like toes. It really was made of wood, Alice saw – here and there along its barky surface, she could see thin, protruding twigs and even a few hanging leaves.

It sat motionless for a while, glaring at her with its brilliant green eyes. Alice wasn’t quite sure what to do. She was supposed to kill the thing, Geryon had said, but she had never deliberately started a fight with anyone in her life, and hadn’t the least idea how to go about doing it. Instead she cleared her throat and held out her palms in what she hoped was a non-threatening manner.