Sam Hunter (Melissa George), an operative for the elite private intelligence and security firm Byzantium, is finishing a mission in Tangier when an attempt on her life leaves her critically injured. Not knowing who tried to kill her, she disappears to a remote location to recover, regroup and retrain. Returning to work unannounced nearly a year later, Sam surprises her co-workers, who are suspicious about her disappearance, especially Aidan Marsh (Adam Rayner),her secret lover. Her bosses, Rupert Keel (Stephen Dillane) and Deacon Crane (Adewale Akinnuoye-Agbaje), retain doubts about her, but need their best agent for an important new assignment. The team devises a plan to have Sam infiltrate a family headed by powerful millionaire Jack Turner (Patrick Malahide), a man with a criminal past whose ambitions are at odds with Byzantium's secret client.