Following the murder of a Cuban man on a busy street in New York City, Frank Westlake, the chief patrol inspector for the United States Department of Immigration, begins an investigation into the crime and its connection to an illegal alien smuggling racket headed by a man known as Palinov. Meanwhile, in Havana, Cuba, immigration detective Pete Karczag dedicates himself to the capture of Palinov. Posing as a Hungarian refugee desperate to gain entry into the United States, Pete befriends Palinov and offers him money to secure his passage to America. While waiting for Palinov to introduce him to a smuggler, Pete meets Marianne Lorress, a refugee from Vienna who survived internment in a German concentration camp. Late one night, Pete walks by a nightclub just as Marianne is being arrested for taking employment there without working papers. Thinking fast, Pete wins Marianne's release by posing as her husband. When one of Palinov's henchmen, Harry Nordell, discovers that Pete is really an American agent, he knocks him unconscious and reports his discovery to Palinov. Though Palinov later tells Pete that he knows who he is, Pete vows to continue his search for evidence. Later, however, Pete, having fallen deeply in love with Marianne, makes plans to resign from his job so that he may stay in Cuba and continue his romance. Marianne leaves Pete when Palinov tells her that he is an American immigration agent. Harry is given orders to kill Pete, but Pete manages to overpower him and then forces him to confess that a man named Archer Delby James is the pilot who will be flying Palinov's plane to the United States later that night. After informing Westlake about the illegal flight and its pilot, Pete returns to the United States to help plan the interception of the airplane. Meanwhile, Palinov, realizing that immigration officials are closing in on him, decides to flee Cuba with the next group that James will be smuggling to the United States. Among the six passengers whom Palinov is smuggling is Marianne, but Palinov plans to make her his captive once they arrive in America. As American Navy planes follow the smugglers, Pete, aware that Marianne is on the airplane, monitors the flight's progress with apprehension. When Palinov and James spot the Navy planes, they attempt to escape capture by crash-landing the plane in the Florida Everglades. After they kill one passenger and abandon the others, Palinov and James take Marianne and attempt a getaway on a small life raft. While Westlake rescues the abandoned airplane passengers, Pete takes a motor boat to the site of the crash and finds Marianne with Palinov. Aware that the gas tank is empty and that Palinov will not be able to escape, Pete then trades his boat for Marianne. Once safely in Pete's custody, Marianne accepts the penalty for entering the country illegally, but looks forward to a happy future with Pete.