Or another time. I don't quite remember, having read it about 7-10 years ago.
All I remember is a boy that uses a knife to sort of create a magical portal in the air in front of him, by feeling like he is the edge of the knife. He travels between our world and another, or perhaps our time and another time, but I'm pretty sure it's another world. I remember him getting chased once and having to hurry up with the "portal cutting", and I think he had company that time.