Very gradually, Alice became aware that something strange was happening. They were walking in a straight line, not turning any corners or going round any bends, but she had the odd feeling they’d changed directions several times. She looked up at the markers, and tried to remember which way they’d been pointing before. And the aisle they were following went on and on, without ever reaching a wall or an intersection. She already felt as though she’d walked so far, they should have been at the edge of the building.

And, out of the corner of her eye, she thought she could see the shelves changing. Shifting their positions, rearranging themselves in her wake. When she looked at them, they remained reassuringly still, as bookshelves ought to, but as she turned away she could have sworn she saw gaps appear and vanish again, books and shelves sliding apart and together again.

It reminded her of the invisible servants in the house, and all at once she went from being a little afraid to flushed and irritated. She was sick of everything happening behind her back, sick of whatever joke was going on. It’s about time they let me in on it.

Alice walked a few more steps, picking her moment, then whirled abruptly on one foot.

‘What is going . . .’

She trailed off. The path behind her was gone. The aisle continued for a few feet, then dead-ended in a heavy-looking shelf whose layer of dust clearly showed that no one had touched it for decades.

Anger drained away, and fear came flooding back. Alice turned back to the cat. ‘Listen—’

The cat was gone too.

Ahead of her, the aisle came to a row of backless steel shelves, more like pantry shelves than proper bookcases, that were made into a nearly solid wall by stacks of heavy leather-covered volumes. The path turned right, paralleling this row for a few feet before turning again to head back in the direction it had come.

What caught Alice’s attention, though, was the light. It came through the tiny gaps and cracks between the books ahead of her, casting vivid shadows. Someone, on the other side of those shelves, had a lantern much brighter than her own. And there was a sound, a very faint one, that Alice found maddeningly familiar.

Slowly, she set her own lantern on the floor, and crept closer to the shelves. The sound grew louder, a deep droning, almost like an electric fan—