The Dark Vault by V.E. Schwab

Titan Books. Paperback. NEW. Each body has a story to tell, a life in pictures only librarians can read. The dead are called histories, and the realm in which they rest is the archive. Mackenzie's grandfather brought her here when she was twelve years old. Now her grandfather is dead, and Mac has grown into what he once was: a ruthless Keeper, tasked with stopping often-violent histories from waking up. Now Mac knows fear for what it is: a useful tool for staying alive.