Jimmy and Billy are reunited after being separated at birth. Billy decides to open up a marital arts school, to teach local kids. Billy is attacked by the shadow boss, who turns out to be his brother.
Jimmy captures his brother Billy and takes him to the Shadow Master. The Shadow Master orders Jimmy to lock his brother up and before Jimmy can do so, the Shadow Master turns on him. Jimmy sets his brother free and the two transform and escape from the Shadow Master. Jimmy is now one of the good guys.
The Shadow Master has come up with a plan to introduce a new drug to Metro City, called Oblivion. The double dragons, along with Colonel McReady, blow up the drug tanks and foil the Shadow Master's plan.
The Shadow Master begins operating an illegal fighting ring in a secluded area of Metro City. Sickle then forces a homeless martial artist named Vortex to fight in the tournament by holding a group of homeless children hostage. Billy and Jimmy must rescue the children and help Vortex before the Shadow Master can get rid of them.
Jimmy is framed for a bunch of crimes by a crooked police commissioner and is sent to Radica prison. Billy and Marian must free Jimmy before the Shadow Master can get rid of him using a deadly mutant named Hannibal.
Billy and Jimmy meet a powerful chi master named Su Lien and her sumo wrestler student named Tsunami. Su Lien is then duped into helping the Shadow Master reform his evil ways. When the Shadow Master hooks Su Lien up to a virtual reality machine so that he can drain her mind and steal her powers, Tsunami and the Lee brothers team up to rescue her.
