His Dark Materials: The Subtle Knife (Book 2)

The second book in Philip Pullman's His Dark Materials trilogy. Young Will Parry, searching for his missing father, steps through a window into another world where he meets Lyra Belacqua, who is on a quest to understand the mysterious Dust. Together they embark on a dangerous journey and discover a deadly secret — the subtle knife, a blade that can cut through anything, including the fabric between worlds.