The Subtle Knife
Both angels find Will Parry at the end of "The Subtle Knife"; because Will is the bearer of the subtle knife, they hope to bring him to Lord Asriel. However, Will's companion Lyra Belacqua has been kidnapped and Will refuses to go to Asriel until Lyra is found. The angels agree to accompany Will without question until she is found. When Baruch is killed in "The Amber Spyglass", Balthamos, stricken with grief, promises to aid Will in every way possible to honour Baruch's sacrifice. When Balthamos is unable to do so, he runs away, grieving over Baruch's death and feeling guilty about abandoning Will. At the end of the book, he confronts and kills Father Gomez, an assassin hoping to kill Lyra, and dies himself.