In the heart of New York City, Cassie Andrews's quiet life as a bookseller is upended when she inherits a magical tome known as the Book of Doors from a beloved customer. The book grants her the ability to turn any door into a portal, leading her into a hidden world where books wield ancient power and are worth killing for. Cassie, alongside her best friend Izzy and the enigmatic Drummond Fox with his secret library, becomes entangled in a perilous adventure against a nameless evil that will stop at nothing to claim the book's power. As they navigate violence, danger and dark forces, Cassie learns that with the magic of the books comes great responsibility, and that some doors, once opened, can change one's life forever.