"Mike" (Tyrone Power) is a US State Department courier who is sent on a routine, but dangerous, mission to Trieste where he is to rendezvous with a passenger on a train then collect and repatriate an important document. Of course, the Soviets are also on the trail of this transaction and when it all goes wrong, "Mike" finds himself embroiled in something far more sinister than he has experienced before. He is now at the behest of his new military handler "Col. Cagle" (Stephen McNally) and his wily sergeant "Guelvada" (a lively effort from Karl Malden) as he must try to find which of two women ...