While looking for a cat, Ryo and Robert (two karate experts) witnessed a murder related to a stolen diamond. After fighting the murdering mobsters, they discovered that the top mobster, Mr. Big, had kidnapped Ryo's sister to exchange her against the diamond, which he believes to be in the possession of the protagonists. They then have to defend themselves anyway they can - mainly through kicks and punches. They both attempt to break into Big's hideout to save Yuri but their plans are foiled by the sudden arrival of the police force. Forced with no other options, they spend the night searching for the diamond. When they find it, they go to meet Big and give it to him. A big fight ensues, complete with an exploding helicopter and a bout with King and Big, but they are able to save Yuri and h