A seaport murder alerts Inspector Erskine (Efrem Zimbalist Jr.) to the presence of Communist spies in the area. Sure enough, enemy agent Conrad Letterman (Michael Rennie) is laying the groundwork for a plan to blow up a military supply ship bound for the Orient. In order for the mission to succeed, Letterman must put pressure on a pair of "sleeper" agents, John and Viv Caldwell (Arthur Franz, Phyllis Thaxter), who are no longer devoted to the Communist cause. ~ Hal Erickson, Rovi