His Dark Materials Series by Philip Pullman

His Dark Materials Series by Philip Pullman - The series follows Lyra Belacqua and Will Parry as they journey across parallel universes, confronting cosmic forces and uncovering deep truths about consciousness, free will, and the nature of the soul.

• The Golden Compass:
  Lyra discovers a secret about kidnapped children and travels north to rescue her friend, uncovering a cosmic mystery.
• The Subtle Knife:
  Lyra meets Will, a boy from another world, and together they explore new realms while pursued by powerful enemies.
• The Amber Spyglass:
  Lyra and Will must journey to the land of the dead and make a great sacrifice to save all worlds from oppression.