Sometime in the mid-1960s, mercenary Bruce Curry (Rod Taylor) is hired by Congolese President Ubi (Calvin Lockhart) supposedly to rescue the European residents of an isolated town about to be attacked by rebel Simba Rebellion in the Republic of the Congo (Léopoldville). But in reality his mission is to retrieve diamonds, worth fifty million dollars, from a mine company's vault. Curry's subordinates include his friend Ruffo (Jim Brown) and alcoholic Doctor Wreid (Kenneth More). He also reluctantly recruits ex-Nazi Henlein (Peter Carsten) because he needs his military expertise and leadership skills.