I stood and took a step back – and the cold vanished. Feeling all electrified with nerves, I squatted again and felt around the air. A perfect tall square of sharp coldness started about a metre above the box and ended right on one side of the lid. The air next to it was as warm as anything.

The cat wound herself round my legs again and again; I’d almost forgotten about her. Then, all quivery and happy, she jumped on to the box and pawed over twigs and dead ivy as neat and light as a dancer, as if tracing her paws over steps drawn out beforehand. This was obviously one of her favourite places. When she came to the cold part, she stopped. Her skin rippled and twitched.

Then, like she’d wound around my legs, the cat rubbed herself against part of the lid of the thing and something came loose. She pushed her head against the wires, as if the box itself was going to feed her. And then the thing that was always going to happen happened: the stupid cat butted the loose part off completely.

It made a heavy thud on the undergrowth, louder than you’d believe possible from the size of it, and the cat jumped off, all scared, as if she hadn’t even done anything.

I poked the loose part with my toe – it was a metal bar – and then I left it there. Didn’t know what else to do. Couldn’t make sense of where it fit or what it might be for—

A tiny noise came from the box.

A movement.

Something was inside. Something bigger than a moth.

My head and neck tingled. The thing inside moved again; something was definitely trapped. Could an animal have got into a moth trap somehow? The cat sat on a tree root, staring at me, calm now. Waiting.

I felt for the fastenings. Really shouldn’t …

But I couldn’t leave an animal to suffer and maybe die. There were no fastenings. No ordinary ones, anyway. And nothing budged when I pulled a metal loop on the front edge. I bent down still further and squinted through a crack where the side joined the top. The body of a spider lay millimetres from my eye, squashed as flat as if it had been ironed.

Another tug on the corner of the lid and something loosened. Now each tug made a creaking, splintering noise. A smell of rusty metal and damp and toadstools seeped out. I looked behind again, listening for footsteps, then pulled more gently. After a while, the lid opened a crack. It couldn’t have been more than a centimetre, but in that tiny space everything changed.

The whole box buzzed. I jumped away, but not before a tiny stingy-burning feeling got me on the forehead. My hair rose in the air on its own. The whole box crackled, and for a microsecond, my teeth fizzed.