In 1878, the shortest trail West through the Arizona territory passed by the foot of Bailey Mountain. Although the shortest, it also was the most dangerous route because Bailey Mountain was the stronghold of a band of renegade Apache, led by Chief Diablito. A group of land surveyors is attacked and massacred by Diablito's renegade Apache. The Indians abduct Mary Carlyle, the daughter of General Carlyle. As a result of this, Major C. E. Breverly, commandant of the nearby cavalry outpost sends a scout to find prospector and Indian guide Ward Kinsman. Kinsman is secretly mining for gold near Bailey Mountain, under the nose of Chief Diablito. At the cavalry outpost, Major Breverly requests Kinsman's assistance in saving Mary Carlyle from the Apache. Mary's sister, Ann Duverall, also demands her sister's immediate rescue but Kinsman, fearing a great loss of troopers in a confrontation with the Apache, refuses. Not being on the army's payroll allows him to refuse assignments. However, he later changes his mind when he falls for the beautiful Ann Duverall who's engaged to Captain Ben Lorrison. At the outpost, Tom Conovan, an alcoholic cavalryman frequently abuses his wife, Martha. She's having an affair with Lt. Linus Delaney who encourages her to leave her abusive husband. The affair leads to gossip and that causes frictions within ranks. Scout Ward Kinsman, leading a small scouting troop, picks up the trail of Diablito. The scouting party discovers a small group of Apache, mostly women and children. The cavalrymen raid the group of Indians and capture prisoners who, under questioning, reveal the location of Diablito's band. It's also learned that Mary Carlyle is indeed held by Diablito and that she's unharmed. At the outpost, the officers plan an expedition meant to surround and capture Diablito's renegade band. It is assumed that he will try to escape across the border into Mexico. Therefore, two cavalry troops are tasked to converge on Bailey Mountain from opposite directions in order to prevent Diablito's escape. The plan counts on the element of surprise but the Apache outnumber the cavalrymen by 3 to 1.