Will, still watching, saw the cat behave curiously.
She reached out a paw to pat something in the air in front of her, something quite invisible to Will. Then she leapt backwards, back arched and fur on end, tail held out stiffly. Will knew cat-behaviour. He watched more alertly as the cat approached the spot again, just an empty patch of grass between the hornbeams and the bushes of a garden hedge, and patted the air once more.
Again she leapt back, but less far and with less alarm this time. After another few seconds of sniffing, touching, whisker-twitching, curiosity overcame wariness.
The cat stepped forward, and vanished.
Will blinked. Then he stood still, close to the trunk of the nearest tree, as a truck came round the circle and swept its lights over him. When it had gone past he crossed the road, keeping his eyes on the spot where the cat had been investigating. It wasn’t easy, because there was nothing to fix on, but when he came to the place and cast about to look closely, he saw it.
At least, he saw it from some angles. It looked as if someone had cut a patch out of the air, about two metres from the edge of the road, a patch roughly square in shape and less than a metre across. If you were level with the patch so that it was edge-on, it was nearly invisible, and it was completely invisible from behind. You could only see it from the side nearest the road, and you couldn’t see it easily even from there, because all you could see through it was exactly the same kind of thing that lay in front of it on this side: a patch of grass lit by a street light.
But Will knew without the slightest doubt that that patch on the other side was in a different world.
He couldn’t possibly have said why. He knew it at once, as stongly as he knew that fire burned and kindness was good. He was looking at something profoundly alien.