Rigby, a government agent investigating an arms surplus racket on the Central American fishing island of Los Trancos, falls in love with one of his suspects, café singer Elizabeth Hintten.  While considering his affair with Elizabeth, Rigby recalls the day in Washington, D.C., when his boss, Gibbs, first briefed him on the case: Gibbs tells Rigby that a group of racketeers have been diverting war surplus items and airplane motors to Central America, where they are refitted and sold for profit.

Assigned to locate the motors and raid the racketeers' headquarters, Rigby is told that the government suspects Elizabeth and her alcoholic war veteran husband Tug.  After arriving in the Los Trancos town of Carlota, Rigby, posing as a sportsman, finds Elizabeth singing at Pedro's nightclub and befriends her.  Rigby and Elizabeth soon strike up a romance, though Tug is either too drunk or too busy to notice.

One night, at a bar, Rigby is approached by J.J. Bealer, a waterfront thief, who, after telling Rigby that he knows about his investigation, offers him $10,000 to leave the island.  Rigby rejects the bribe, and soon comes to suspect that a man named Carwood, who is posing as a mine owner, is somehow associated with Bealer.  The following day, in order to learn more about Carwood, Rigby joins him on a fishing trip.

The fishing expedition nearly proves fatal for Rigby when Carwood deliberately causes the fishing boat to lurch forward while Rigby is standing near the edge.  Rigby is falls into the water, but Emilio Gomez, the boatman, jumps into the water and saves him.  Emilio, however, is killed by a shark while trying to swim back to the boat.  A short time later, Emilio's father Pablo confirms Rigby's suspicions that Carwood is the mastermind of the smuggling operation, and, angered by his son's death, volunteers to help Rigby investigate the men responsible.

As Rigby comes out of his reverie, he is still torn between his love for Elizabeth and his obligation to investigate her.  His decision is to save Elizabeth from prosecution by accepting Bealer's bribe and fleeing from the island with her.  However, before Rigby can tell Elizabeth his plan, Bealer convinces Elizabeth that her husband is a criminal and that Rigby is an investigator who intends to put him in prison.  In the hope of saving Carwood's illicit operation, Tug enlists Elizabeth's help in drugging Rigby long enough to allow all those involved in the smuggling ring to flee.

Rigby loses consciousness soon after drinking a cocktail tainted with a heavy sedative, but Elizabeth immediately feels remorse for what she has done.  Carwood, meanwhile, murders Tug for talking too much, and makes preparations to flee.  Rigby regains consciousness sooner than Carwood had anticipated, and sets out in search of his suspects.  When Rigby tries to arrest Carwood, Carwood shoots Bealer and escapes into a crowded carnival.  After killing Carwood, Rigby resumes his romance with Elizabeth, whom he now knows to be innocent.