While attempting to rescue a cat, martial artist Ryo Sakazaki and his playboy best friend Robert Garcia inadvertently break into a jewel thief's apartment. Shortly after entering, they witness the thief being murdered by a group of thugs. Although they fight their way out and escape, the situation deteriorates when Ryo and Robert discover that the thugs were working for Mr. Big, the most powerful crime boss in South Town. Mr. Big not only believes that the two have stolen the "Eye of Sirius," a priceless diamond, but he has also kidnapped Ryo's younger sister, Yuri, and is holding her hostage. Lacking the diamond and with no other options, Ryo and Robert must fight through Mr. Big's men to save Yuri before it is too late.