No one knows Margo's real name. Her colleagues and patrons at a small-town public library only know her middle-aged normalcy, congeniality and charm. They have no reason to suspect that she is, in fact, a former nurse with a trail of countless premature deaths in her wake. She has turned a new page, so to speak, and the library is her sanctuary, a place to quell old urges.
That is, at least, until Patricia, a recent graduate and failed novelist, joins the library staff. Patricia quickly notices Margo's subtly sinister edge and watches her carefully. When a patron's death in the library bathroom offers a hint of Margo's mysterious past, Patricia can't resist digging deeper - even as this new fixation becomes all-consuming.