The Subtle Knife by Philip Pullman

The excerpts narrate the journey of Will, a young boy who protects his mentally ill mother from mysterious men before running away, acquiring a magical subtle knife, and entering a parallel world. There, he teams up with Lyra Silvertongue, who possesses an alethiometer (a truth-telling device) and is pursuing knowledge about Dust, a substance linked to consciousness, while being pursued by the menacing Mrs. Coulter and others from her world. Meanwhile, the witch Serafina Pekkala and the aeronaut Lee Scoresby search for Lyra and investigate the activities of Lord Asriel, Lyra's father, who is amassing forces for a celestial war against the governing religious authority known as the Magisterium. The story details Will's dangerous encounters, including a fight where he loses two fingers, and Lee Scoresby's meeting with the explorer Stanislaus Grumman—revealed to be Will's missing father, John Parry—who tasks Will with carrying the subtle knife to aid in the coming conflict.