An ancient sect. A modern mystery. The most dangerous secret ever unearthed. Antiquarian bookseller Robin Jessop has acquired a strange medieval volume. What appears to be a book is a cleverly disguised safe, in which she finds a single rolled parchment, written in code. For encryption expert David Mallory, the text is impenetrable. Until an invaluable clue opens the door to a conspiracy, stretching back seven centuries.