Lucas boards a boat heading from Tangier to Plymouth to track a Somali terrorist, and is saved from danger by Beth Bailey, an undercover mercenary posing as a sex worker. When it emerges that the vessel is carrying an explosive payload, the team fears the launch of the newest addition to the Royal Navy's fleet is the target. Beth's arrival at section D brings new information and feelings of familiarity to Harry, who is forced to put aside his concerns about the source and take drastic action. Sophia Myles (Moonlight) joins the cast, with Peter Firth and Richard Armitage.