The Unbound By Victoria Schwab

Each body has a story to tell, a life seen in pictures only Librarians can read. The dead are called Histories, and the vast realm in which they rest is the Archive.
Last summer, Mackenzie Bishop, a Keeper tasked with stopping violent Histories from escaping the Archive, almost lost her life to one. Now, as she starts her junior year at Hyde School, she’s struggling to get her life back. But moving on isn’t easy, not when her dreams are haunted by what happened. She knows the past is past, knows it cannot hurt her, but it feels so real. When her nightmares begin to creep into her waking hours, she starts to wonder if she’s truly safe.
Meanwhile, people are vanishing without a trace, and the only thing they seem to have in common is Mackenzie. She’s sure the Archive knows more than they are letting on, but before she can prove it, she becomes the prime suspect. Unless Mac can track down the real culprit, she’ll lose everything: not only her role as Keeper, but her memories – and even her life. Can Mackenzie untangle the mystery before she herself unravels?