A merchant marine seaman is found murdered and suspicion falls upon the operator of a dime-a-dance honky tonk joint. A federal undercover agent is planted in the place to gather evidence, and he soon learns that the dive is only a cover-up for diamond-smuggling activities, and that one of the operation's henchmen, who is handy with a switch-blade knife, is the killer. Before they can be arrested, the henchman kills his boss and is shot while trying to escape.