The Underhill Library is a place of mystery for sixteen-year-old Alvy when she becomes the Assistant Librarian. She can see faeries and she thinks that she understands the library’s inner workings because she knows that the Librarian is a faery and that the Page Master, Underhill, was once human. The Librarian Pereaux is the Great Emissary for the ruth faery Queen of the Seelie Court, but Alvy doesn't fully realize what Pereaux's role in the Ethereal Realm entails. When the Bridge between the faery realm and the human world begins malfunctioning, a group of renegade faeries start conjuring their own portals, entering the human world without permission, and bringing with them a world of magic, faeries, stolen souls, and uncovered pasts that were meant to be left hidden. It is up to a group of unlikely comrades to apprehend the perpetrators, and as these companions make mistakes, make deals, and find love, they come to realize that they don't always have to fight their battles alone.