American Steve Kendall, a freighter's radio officer, discovers seaman Carlson sending an unauthorized message ashore as the ship approaches his war-poised homeland. Carlson is shot in cold blood when he jumps ship and Kendall, implicated in the espionage, swims ashore to avoid arrest. A woman he meets at the dock hides him in her apartment, where he learns Carlson was her brother, and they both work in a sabotage ring. Nedra is a singer at Tio's Cafe, and she approaches Tio for help when both the saboteurs and the secret police try to capture Steve.