Mallory Bright is the only daughter of London's most ingenious locksmith and has apprenticed with her father since childhood. After scandal destroys her reputation, Mallory has returned to her father's home and lives almost as a recluse, ignoring the whispers of their neighbors. But Sir Francis Walsingham, Queen Elizabeth's spymaster and a frequent client of Mallory's father, sees potenial in Mallory and draws her into his world of danger and deception. The locksmith's daughter is not only good at cracking locks, he discovers; she also has a talent for codes, spycraft, and intrigue. With Mallory at his service, no scheme in England or abroad is safe from discovery. But Mallory's loyalty wavers when she witnesses the brutal and bloody public execution of three Jesuit priests and realizes the human cost of her espionage. And later, when she discovers the identity of a Catholic spy and a conspiracy that threatens the kingdom, she is forced to choose between her country and her heart. Once Sir Francis' greatest asset, Mallory is fast becoming his worst threat - and there is only one way the Queen's spymaster deals with his enemies...