Book of Secrets

The Book of Secrets is the end-game reward trophy for the Nightfall campaign.

Acquisition

 * Keeper of Secrets in Throne of Secrets (only accessible by completing the Abaddon's Gate mission)

Each character can only receive 1 book in this manner, although they can be traded between characters.

Collectors

 * Keeper of Shadows
 * Keeper of Steel
 * Keeper of the Elements
 * Keeper of Nature
 * Keeper of Light
 * Keeper of Bone
 * Keeper of Spirits
 * Keeper of Illusion
 * Keeper of the Scythe
 * Keeper of the Spear