The young William Parry is looking for his long-gone father. After he probably killed a man, he flees and crosses a hidden dorway to a parallel world. There, in the city of Cittàgazze, he meets Lyra, the heroin of Northern Lights. Just like him, she is also struggling to find her father back and just like him, she also has a mission she has no idea of. Together, Lyra and Will will have to face dark opponents to reach their goals and enter the mysterious Tower of Angel and find the mighty Subtle Knife.