Roland, a low-grade Fixer from a location known only as the City, one day finds himself transported into the foyer of the titular Library, a mysterious location filled with books on any subject one could think of. He soon meets the Head Librarian Angela, and after a brief scuffle, she decides to spare him and recruits him to be her guide on the outside world. Angela has a strange way of going about it though, as she sends out calling cards called Invitations to ask people to come to the Library and gives them a choice in whether they accept or decline. If the guests accept, they must survive mortal combat against the Librarians that guard the building; if they win, they can take any book they want. If they lose, they will become a book themselves. All of this is in service to Angela's goal — gaining the one "perfect" book that can make her into a human.