The Amber Spyglass (His Dark Materials #3)

The Amber Spyglass is the third and final novel in the His Dark Materials series, written by English author Philip Pullman, and published in 2000.
At the end of The Subtle Knife, Marisa Coulter captured Lyra. She has now relocated her to a remote cave to hide her from the Magisterium, who are determined to kill Lyra before she yields to original sin. In order to keep her hidden, Marisa forces Lyra to drink drugged tea that puts her to sleep. While deeply asleep, Lyra dreams that she is in a wasteland (later realized as the land of the dead) talking to her deceased friend Roger Parslow, whom she promises to help.
In Cittàgazze, two angels, Balthamos and Baruch, tell Will, the bearer of the Subtle Knife, that they are taking him to Lord Asriel. Will refuses to go until Lyra is rescued, to which the two assent. However, they are attacked by a soldier of the archangel Metatron, and Will uses the knife to cut a window into another world to escape. Baruch flies to Lord Asriel to tell him what has happened and to get help.