Young Dave McVey (James MacArthur) arrives on a South Pacific island after the enemy strikes. When bandits raid the plantation owned by his family, Dave is saved by Manuel Careo (Leopoldo Salcedo), who takes him to the barrio of Viray, where patriots are organizing to fight. Here Dave meets Pinang (Marilou Munoz), Viray's young and pretty granddaughter, and Joe Trent (Van Heflin), amoral and brutal, who soon, under the influence of liquor, attacks Pinang. Now both he and Dave flee. In the jungles, they meet a band of natives led by Atong (Oscar Roncal), a tough, ruthless native. Accompanying Atong is Sisa (Rita Moreno), beautiful and vibrant, who speaks English. All go to the camp of Colonel Ryker (Sidney Clute), commander of a small group of Americans. Here Joe and Dave receive instruction in jungle fighting. Later Dave meets Vera (Liza Moreno), a camp follower, who guides him along another step on the path to manhood. Soon Atong is revealed as a bandit, who has joined the hell-blasters only to get guns for his band. And he reverts immediately into the type that has raided native villages for years. Sisa had been forced to join him. Joe is not averse to working with Atong. He also has an affair with Sisa. Dave, suddenly taken with fever, has no choice but to go along, while Sisa tries to nurse him back to health. Several barrios are raided. At one, where the killing is particularly ruthless, Joe shoots Atong and takes over. Meanwhile Dave and Sisa fall in love. Careo appears to charge Joe with attacking Pinang and the responsibility for raiding villages. Joe tries to brazen it out. When Careo asks Dave to sign a statement against Joe, Dave refuses. Then an enemy tank attacks. Joe is wounded, yet he, Dave and Sisa escape. While Joe is camp ridden, Dave searches for their allies. In his absence Joe forces his atttentions on Sisa again. When Dave learns of this, he fights Joe. As the trio make plans for their next move, they find that Careo and three of his men have followed him. Joe is determined to kill Careo. During the battle Dave finally has to make his choice -- he shoots Joe to save Careo. He and Sisa are then free.