In 1867, after the Civil War, a craggy exConfederate States Army officer, Jim Lassiter (Richard Boone), has set out for revenge against Apache Indians who massacred his family. He kills some Apaches with a U.S. Army repeating rifle.

A patrol headed by Army Captain Haven (Stuart Whitman) and Buffalo Soldier Sergeant Franklyn (Jim Brown) is sent to investigate the theft of 2,000 rifles from a U. S. Cavalry command. The trail leads to Lassiter, who owns one of the stolen rifles, but he refuses to reveal the name of his contact, and is jailed with a knifewielding womanizing Mexican prisoner, Rodriguez (Tony Franciosa), a murderer. Haven plans to take a wagonload of gunpowder to Mexico, hoping to use it as bait for those who stole the rifles.

The U.S. Army offers Lassiter an exchange for his freedom if he leads a small, clandestine scouting unit into Mexico consisting of Captain Haven, Sergeant Franklyn, and Rodriguez, to Pardee, the man from whom he obtained the rifle. Lassiter feels that the Apaches have proven formidable with lesser weaponry, and has a cause for concern should they become equipped with such superior firepower, and finally agrees.

Captain Haven and his patrol have skirmishes with Indians and bandits. Danger, mistrust and hostility are their only companions. Along the way they pick up a young Apache Indian woman warrior, Sally (Wende Wagner). Lassiter, who hates Indians because they killed his family, wants to kill her, but they learn from her that Pardee is about to sell the rifles to Apaches.

After blasting their way through bandits and Apaches, they discover another former exConfederate rebel soldier, megalomaniacal Colonel Pardee (Edmond O'Brien). Pardee was Lassiter's commander during the Civil War, and is still fighting the war from Mexico. Pardee has set up a new Confederate headquarters in Mexico, and is selling guns to the Apaches, including the ones who slaughtered Lassiter's family.

The traitorous Rodriguez escapes, but Lassiter finds and kills him. Lassiter begins talks with Pardee, but when the Indian who killed his family, Bloodshirt (Rodolfo Acosta), appears, Lassiter goes berserk and attacks him. Pardee imprisons Lassiter, Haven, and Franklyn, but Sally frees them, saving their lives, while Pardee negotiates with Bloodshirt. So, Lassiter puts aside his hatred.

While holding off Pardee and his men, Lassiter and Franklyn sacrifice their lives to ignite the gunpowder wagon, destroying the camp and killing everyone, to save Captain Haven and Sally, who return to Texas.

A 1964 American Western film directed by Gordon Douglas, produced by
David Weisbart, screenplay by Joseph Landon and Clair Huffaker, based on Clair Huffaker's novel "Guns of Rio Conchos" published in 1958, cinematography by Joseph MacDonald, starring Richard Boone, Stuart Whitman, Anthony Franciosa, Edmond O'Brien, and Cleveland Browns halfback Jim Brown makes his screen debut. He gave up his football career, at its peak, to try acting. Wende Wagner also makes her screen debut, in a black wig, and has no English dialogue, later to enter pop culture history as the loyal assistant to "The Green Hornet" on TV.

A CinemaScope production filmed in De Luxe Color from 20th Century Fox. MacDonald's photography and Douglas' use of the scenery make the landscape the big character here. Douglas' long shots reveal miles of vistas, then knows when to pull in close to envelope the characters to give off the feeling of mental claustrophobia.

Huffaker's novel is reminiscent of the John Wayne films "The Comancheros" (1961), another Fox movie that also starred Stuart Whitman for which Huffaker cowrote the screenplay, and "The Searchers (1956).

Pardee (Edmond O'Brien) explains his war tactics in a way that foreshadows Colonel Kurtz in Francis Ford Coppola's "Apocalypse Now" (1979). Pardee admires the enemy's ruthlessness and plans to create an army like that of his own.

This story about two men who won't let go and keep seeking vengeance was released while Franciosa was starring on an ABC sitcom called "Valentine's Day." To help publicize the picture, Franciosa comedically recreated his Rodriguez character in one episode. Both the feature and the series were produced by 20th CenturyFox.

When the US Government commenced its war against the Comanches after the American Civil War, the "Comancheros" supplied firearms and ammunition to the tribes. In the winter of 1874–1875, US Army troops under General Ranald Mackenzie attacked and defeated five camps of Comanches in Palo Duro Canyon. This defeat caused the last band of the freeroaming Comanches, the Kwahada under Quanah Parker, to surrender, and brought an end to the 100 year old Comanche and Comanchero trade relationship.

This rugged western film was considered groundbreaking as the two leads were both Jewish. Gritty and well written, one of the last of the "Great Action Westerns" with enough action to satisfy the biggest western fans around. This is a mustsee!