The Bureau is based upon real accounts by former spies and inspired by contemporary events, and centres on the daily life and missions of agents within France's Directorate-General for External Security, its principal external security service. It focuses on the "Bureau of Legends", responsible for training and handling deep-cover agents (operating 'under legend') on long-term missions in areas with French interests, especially in North Africa and the Middle East. Living under false identities for years, these agents' missions are to identify and recruit good intelligence sources.