"The Subtle Knife" is the second book in Philip Pullman's His Dark Materials trilogy. It follows the journey of Lyra Belacqua, who meets Will Parry, a boy from our world. Together, they explore parallel universes and face various challenges, including dangerous creatures and powerful forces. The story introduces the Subtle Knife, a magical tool that can cut through the fabric of reality, allowing access to different worlds. As Lyra and Will navigate their adventures, they uncover secrets about their destinies and the larger battle between good and evil that looms over their lives.