Curry (Rod Taylor) is a veteran soldier-of-fortune hired by the president of the Congo for a three day mission. He and native Congoan Ruffo (Jim Brown) are to oversee the safe passage of a train through hostile enemy territory and bring back some uncut diamonds and a human cargo of fugitives loyal to the Congo cause. The two employ the drunken Doctor Wreid (Kenneth More) and a suspicious ex-Nazi named Henlein (Peter Carsten). The quartet, along with 40 of the Congo's best soldiers, try to maneuver the train against the rebel forces and save the beautiful missionary Claire (Yvette Mimieux) at no extra charge. The action takes place in the wake of the political unrest that swept the Congo in the 1950s.