The Dark Archieve (The Invisible Library #7 )by Genevieve Cogman

A professional spy for a mysterious Library which harvests fiction from different realities, Irene faces a series of assassination attempts that threaten to destroy her and everything she has worked for.

Irene is teaching her new assistant the fundamentals of a Librarian's job, and finding that training a young Fae is more difficult than she expected. But when they both narrowly avoid getting killed in an assassination attempt, she decides that learning by doing is the only option they have left - especially when the assassins keep coming for them, and for Irene's other friends as well...