A military train guarded by American soldiers and Japanese police is robbed of its cargo—guns, ammunition, and smoke bombs. During the raid, a U.S. Army sergeant guarding the train is shot and killed. Five weeks later, a thief named Webber Biff Elliot lies dying in a Tokyo hospital, shot by one of his own cohorts during a holdup in which smoke bombs were used. Army investigators discover Webber was killed by the same P38 pistol that killed the sergeant during the train robbery. Webber is questioned by military and police investigators, who discover among his possessions a letter from an American named Eddie Spanier, who wants to join Webber in Japan after his release from a U.S. prison. Though Webber refuses to implicate his fellow gang members, he does reveal that he is secretly married to a Japanese woman named Mariko Nagoya, Yoshiko Yamaguchi // Mariko Nagoya.
Three weeks later, Eddie Spanier arrives in Tokyo and makes contact with Mariko Nagoya, Yoshiko Yamaguchi who uses her trust to help him learn what happened to Webber after seeing a photograph of Eddie with Webber. Eddie learns about Webber’s death and asks Mariko to live with him as his “kimono girl,” a move that deepens their bond even as he continues to operate undercover. He soon tests the waters with a local racket, going to a pachinko parlor and attempting to shake down the manager, only to be beaten by a group of Americans led by Sandy Dawson, Brad Dexter who becomes intrigued by Eddie’s nerve and later offers him a place in his gang, a cadre of disgruntled former servicemen who have been dishonorably discharged.
To solidify his cover, Eddie secretly meets with U.S. and Japanese investigators, while Mariko agrees to stay close and help him in his dual quest: to uncover Webber’s killers and to bring the gang to justice. Mariko and Eddie grow closer as they navigate the danger of being watched by both police and gang members, and Eddie’s deception gradually reveals itself to more players, including Charlie, DeForest Kelley, one of Sandy’s men, who spies Mariko meeting with the American officer to fill him in on the Dawson gang’s next heist.
A key informant, Ceram, Sandro Giglio, informs Sandy that the police are closing in and that Eddie is a military plant. This revelation triggers a dramatic reversal: Sandy orchestrates a fake robbery to trap Eddie, but the plan backfires when Charlie is shot while trying to keep Eddie upright. The pursuit drives Eddie and the police to a rooftop amusement park, where a tense gunfight erupts. In the end, Eddie shoots and kills Sandy, and the pair—Eddie and Mariko—are finally reunited.
