"The Subtle Knife" is the second book in Philip Pullman's His Dark Materials trilogy. It follows the journey of Lyra Belacqua, who meets a new character, Will Parry, in a parallel universe. Together, they explore the concept of multiple worlds and the mysterious substance known as Dust. The story introduces the Subtle Knife, a powerful tool that can cut through the fabric of reality, allowing access to different dimensions. As Lyra and Will navigate their adventures, they confront various challenges, including the pursuit of Specters and the enigmatic Magisterium, which seeks to control knowledge and power across worlds.