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 mystery, and a conspiracy, stretching back seven centuries. Now Jessop and Mallory find themselves on a desperate hunt that could change history, topple an empire and bury them both alive. Because soon they’re not only the hunters. They’re also the hunted.