I read this book when I was a child, maybe 15 - 20 years ago. I really want to find it for my nephew.
I can only really remember the very start of the book, a young boy and his sister are asleep one night and some monsters climb in their window and take the sister.
The story follows the boy as he tries to rescue her, he meets all sorts of fantasy creatures along the way.
The monsters that take his sister have multiple arms and are called, Grabbers or Grabblers or something involving the word grab. I think they are shadows, I remember an illustration on the back of the book and they are completely black and featureless.
I'm pretty sure the book was written by an English author, the name Night-Dreams is in my head for some reason, but I'm not sure why.
That's really all I have to go on, if someone could figure it out I'd very much appreciate it.