After observing war game manoeuvers as a referee, U.S. Marine Major Greg Donahue is posted to Da Nang, South Vietnam for his second tour of duty. He hears that his physician brother Gary has been seen alive in the area after being captured by the Viet Cong. Donahue is accompanied by a Marine Sergeant, an American Priest who was formerly an Army chaplain in the Korean War and a Vietnamese guide to free his brother.