investigators Jim McLain and Mal Baxter come to Hawaii to track American Communist Party activities. They are interested in everything from insurance fraud to the sabotage of a U.S. naval vessel and plans to have local unions go on strike to prevent the loading and unloading of ships on the Honolulu docks. After receiving useful information from reporter Phil Briggs, the agents begin searching for Willie Nomaka, a former party treasurer, who has allegedly experienced a nervous breakdown and is being treated by psychiatrist Dr. Gelster. The doctor's secretary, Nancy Vallon, is helpful as well. McLain asks her on a date and a romance develops. Nomaka's landlady, Madge, assists in the investigation, flirting with McLain. Nomaka's ex-wife also helps McLain. Nomaka is eventually found under another name in a sanitorium, heavily drugged and unable to speak. Party leader Sturak gives orders to Dr. Gelster to get rid of him but McLain rescues Nomaka and takes him to safety. However, two of the communists kidnap Baxter and Gelster accidentally kills him by giving him an injection of truth serum. Sturak orders the members of the communist cell to attend a meeting. Sturak orders Gelster to confess his Party membership to the authorities and identify several non-essential members of the "cell" so that government will believe that the cell has been destroyed and the others can continue their work. The meeting is interrupted by McLain who punches out one of the communists after the communist uses the "N-word." McLain is losing the brawl that follows when the police arrive and place the communists under arrest. The men responsible for Baxter's death are convicted of murder, but ultimately McLain and Nancy Vallon see the others plead the Fifth Amendment and go free.
Several of the people cast in the film were Honolulu citizens: Honolulu Chief of Police Dan Liu, news reporter Vernon "Red" McQueen, wrestling champion Zinko "Lucky" Simunovich, University of Hawaii professor Joel Trapido, Bishop Kinai Ikuma, Sam "Steamboat" Mokuaki, Charles "Panama" Baptiste, Rennie Brooks, Akira Fukunaza and Ralph Honda.
A title card at the end of the film states that the incidents in the film were based on the files of the Committee, although names and places were changed, and acknowledges the cooperation of the Committee in the making of the film.
Nancy Olson hated the script but figured that six weeks in Hawaii and a chance to work with a star like John Wayne seemed a good enough reason to accept. She thought the film would flop and nobody would see it. She was right to a degree – it wasn't one of Wayne's more successful pictures – but she didn't count on how often it would appear on television. She later said people stopped her all the time to mention it. Olson, a staunch liberal Democrat, said she and Wayne would often have political arguments but she would always let Wayne have the last word.
John Wayne recorded an advertisement for Camel cigarettes on the set.
In some European markets the film was retitled as Marijuana and dispensed with the communist angle, making the villains drug dealers instead. This was achieved entirely through script changes and dubbing.
The film's publicity slogan was: "He's A Go-Get-'Em Guy for the U.S.A. on a Treason Trail That Leads Half-a-World Away!"
