Because some doors should never be opened.

New York bookseller Cassie Andrews is not sure what she's doing with her life. She lives quietly, sharing an apartment with her best friend, Izzy. Then a favourite customer gives her an old book. Full of strange writing and mysterious drawings, at the very front there is a handwritten message:

This is the Book of Doors. Hold it in your hand, and any door is every door.

Cassie is about to discover that the Book of Doors is a special book - a magic book. A book that bestows extraordinary abilities on whoever possesses it. And she is about to learn that there are other magic books out there that can also do wondrous - or dreadful and terrifying - things.