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.
I promised after
re-reading the first of these that I would get to the second in a couple of months; that was over three years ago. The good thing about this volume is that what had appeared to be entirely a parallel world now turns out to be linkable to our own, from which Will joins the adventure; and there's lots more gutwrenching stuff about parents and children, and treacherous magicians and well-intentioned scientists. But I do agree that it's a huge shame that Lyra, so much the central character of the first book, has her agency largely removed in this one, and there's a real middle-volume-of-the-trilogy feeling about it.