Under the cover of nightfall, a submarine quietly departs the harbor of Casablanca bound for Belfast, Ireland. The mission is to deliver a new type of selective targeting weapon into the hands of the IRA. Armed with this weapon, the IRA will select and assassinate every prominent Member of Parliament without leaving a trace. Unknown to the IRA, the submarine holds additional secrets. One member of the crew is an undercover British agent, but before the submarine reaches Belfast, the agent will be murdered, and his body will be cast into the open ocean. Upon the discovery of the agent's body, it becomes clear that Burton Humphrey was the intended recipient of the agent's final coded correspondence, a message that only Humphrey can decipher. Humphrey does not recognize Clive Dougan as an intelligence agent; he knows him only as a close friend over the past thirty years. This investigation becomes quite personal as Humphrey races against time to stop the breach of other agent identities working undercover within the IRA, and find those responsible for the death of his close friend. A second and equally dangerous aspect of the investigation is to stop the submarine's voyage with its most deadly cargo. Along the course of the investigation, Humphrey realizes he has placed his own safety in grave danger, the safety of the murdered agent's son, as well as that of his close friend and partner, Penelope Skinner.