The Subtle Knife

The Subtle Knife is the second book of the "His Dark Materials" trilogy written by Philip Pullman and first published in 1997.
In the first world that Lyra enters, Lyra meets a boy of 12 years named Will Parry who comes from Oxford of the reader's universe and is escaping from the authorities. Defending his sick mother he has accidentally killed a man.They travel through a silent world to resolve many mysteries. They begin to realize that there is something special about that world.