April - May 1942 Captain John Garrett of the Australian Army has been ordered back to Melbourne from Townsville to investigate a suspected intelligence leak in Central Bureau. Garrett and an American Captain, Al Tucker are placed into the unit ostensibly as intelligence officers with no one, including the current section leader Captain Anthony Myers, aware of their mission. Tucker begins to work against Garrett who desperately tries to track down the spy operating in the city. In doing so he discovers the most closely guarded secret of the Pacific war. As he draws closer to the truth so begins a life and death battle for survival.