The Subtle Knife is the second installment in the His Dark Materials trilogy. It opens with a new character, a boy named Will from the world that we know, not the world we came to know in The Golden Compass, where everyone has a daemon. Will knows how to disappear, but not with magic. His father has disappeared on a trip to the Arctic, and people are looking for him.
Will ventures to Oxford in hopes of finding him, but stumbles upon a rip in the world. When he slips through the rip, he ends up in a new world and finds a new companion – Lyra and her daemon Pan. The two continue the adventure as Will learns of Lyra’s world, and she of his.