Ray Caldwell, an agent of the ultra-secret government department known as Sector Three, leaves London suddenly, despite an impending mission. This apparent defection causes alarm within The Sector, because of the knowledge that Caldwell carries with him. When he is traced to the Caribbean island of St Lucia, Robert Lane is sent to bring him back, or to silence him if he resists. Lane is reluctant to admit that Caldwell would turn traitor, and when murder blocks his search at every turn he suspects there is another organisation involved. Or is Caldwell himself covering his tracks before selling The Sector's secrets to a hostile foreign power? Lane must discover the truth while his own life is under threat, from an enemy he cannot identify.