Lee (Bruce Lee), a highly skilled Shaolin martial artist from Hong Kong is approached by Braithwaite, a British intelligence agent investigating suspected crime lord Han (Shih Kien). Lee is persuaded to attend a high-profile martial arts competition on Han’s private island in order to gather evidence that will prove his involvement in drug trafficking and prostitution. Shortly before his departure, Lee also learns that his sister’s killer, O’Hara (Robert Wall), is working as Han’s bodyguard on the island. Also fighting in the competition are indebted gambling addict Roper (John Saxon) and fellow Vietnam war veteran Williams (Jim Kelly).
At the end of the first day, Lee is able to make contact with undercover operative Mei Ling (Betty Chung) and after meeting with her, sneaks deeper into Han’s compound looking for evidence. Soon after, he is discovered by several guards and is forced to defend himself before escaping. The next morning, Han has the guards publicly killed by chief guard Bolo (Bolo Yeung) for failing him. After the execution, Lee faces O’Hara in the competition and after an emotional battle ends up killing him. With the day’s fighting over, Han confronts Williams about the identity of the intruder and proceeds to beat him to death when he fails to answer. Later, Han reveals the scale of his drug operation to Roper in the hope that he will join his organization. Despite being initially convinced, Roper refuses after learning the fate of Williams.
Lee sneaks out again that night and manages to send a message to Braithwaite, but is finally captured after a protracted battle with the guards. The next morning Han arranges for Roper to fight Lee, but Roper refuses. As punishment, he is forced to fight Bolo instead but manages to overpower and kill him after a grueling encounter. Enraged by the unexpected victory, Han commands his remaining men to kill Lee and Roper. Facing insurmountable odds, they are soon aided by the island’s prisoners, who have been now been freed by Mei Ling. Lee finally confronts Han in a hidden mirror room and eventually kills him after breaking all the room’s mirrors to reveal his location. Lee returns to the battle which is now over, a bruised and bloodied Roper sits victorious while the military finally arrive to take control of the island.