Shirley, girl friend of a boxer known as "El Tigre" ("The Tiger"), discovers that her brother Lester's life is in danger unless he pays his debts to Chuck, a gangster who uses a nightclub he operates as a front.  Although the debt is considerable, "El Tigre" offers his savings to help Lester pay it off, but Shirley does not want to involve him in her family's problems.

After Lester kills one of Chuck's henchmen, Chuck tries to come to an agreement with Shirley, suggesting that he will forget about his dispute with Lester if she can arrange for "El Tigre" to be drugged and lose his next fight on which he, Chuck, will bet heavily against the favorite.  As Shirley will not go along with this, Chuck enlists the services of Steve, "El Tigre's" manager, who agrees to substitute drugged drinking water during the fight.  However, the police have been tailing Chuck and his gang and, as the fight takes place, confront Chuck and shoot him.

Meanwhile, "El Tigre" easily beats his opponent having accidentally replaced the drugged water with pure water.