An outlaw tries to avoid both his friend, the marshal, and a sadistic bounty hunter in order to hijack a mule train loaded with two million dollars in gold. Based on the novel by Louis L'Armour.

While on the trail of cattle rustler Jedidiah Catlow, Marshal Ben Cowan is ambushed by Indians and shot in the leg with an arrow just as Catlow and his gang come to his rescue. Catlow chuckles when Ben announces that he is under arrest, then passes out from his injury. Catlow, an old Civil War buddy of Ben's, tends to his friend's wounds, and when Ben revives the next morning and again tries to arrest Catlow, Catlow wryly observes that he was not rustling, but merely rounding up "maverick" cattle that belong to anyone who can catch and brand them. Their conversation is interrupted by Orville Miller, a sadistic gun man hired by rancher Parkman to eliminate Catlow. Holding Catlow at gunpoint, Miller announces that he plans to hang him. As Catlow pulls on his boots to "meet his maker," he shoots at Miller with a derringer hidden in one of his boots. In the ensuing gunfire, Catlow and his gang drive away Miller and his men, after which Catlow heads for Abilene, Kansas to sell his herd. Ben follows Catlow to Abilene, but decides not to arrest him because he knows that Parkman will prevent him from receiving a fair trial. To Ben's surprise, Catlow insists upon being arrested and taken to Fort Smith for trial. After Catlow and Ben board the stage to Fort Smith, however, Catlow's gang hijacks it and Mrs. Frost, the sweet old lady who is their fellow passenger, pulls out a gun and orders Ben to release Catlow. Catlow and his men flee to Nogales, a town on the Mexican border, where Catlow reunites with his fiery girl friend Rosita while awaiting the arrival of Sanchez, who is bringing information about a mule train carrying a fortune in gold. Ben and Miller also follow Catlow to Nogales, where Ben urges Catlow to turn himself in before Miller has a chance to kill him. Instead, Catlow proposes that Ben join him in his latest scheme, to round up some "maverick" gold. Soon after, Sanchez arrives with information that the mule train's destination is the Mexican town of Hermosillo, after which Catlow prepares to lead his men out of town. Before leaving, however, Catlow confronts Miller, who is taking a bath, and in the ensuing fight, Catlow smashes Miller with a clay water jug, causing Miller to pass out and land on the shards of the broken jar. Along the trail, Ben sets a trap for Catlow, but the gang outsmarts him, and after capturing the marshal, tie him up and sling him over his horse, then pin his badge to his backside and turn the horse loose. Later, coming upon the helpless Ben, Miller spooks the horse, sending it galloping toward a steep precipice, but Ben manages to untie the ropes with his teeth and stop the animal before reaching the edge and certain death. Soon after, Ben hears a horse whinny, and when he looks up, he sees a wounded young Mexican officer slumped over his horse. The officer, Diego Recalde, tells Ben that he has been attacked by Apache Indians, and as Ben takes the reins of Diego's horse, the Apache attack again, killing both Diego's and Ben's horses. Ben fends off the attack with his rifle, and as Diego joins in with his pistol, the Mexican army comes to their rescue. Meanwhile, Catlow and his gang have hunkered down in Hermosillo in a house owned by Rosita's father, waiting for the mule train to arrive. In gratitude for saving his life, Diego takes Ben to Hermosillo, where his wealthy uncle, General Calderon, owns a grand hacienda. There Ben is smitten by the general's cultured daughter Christina. When the general tells Ben that he is expecting the arrival of a mule train bearing gold found in a cave near the Texas border, Ben deduces that the gold was part of a shipment stolen from the Confederate army during the Civil War. Meanwhile, on the outskirts of Hermosillo, Rafael Vargas, a Mexican army officer in charge of the mule train, is met by one of Catlow's men, who is disguised as a Mexican soldier bearing a fake message from Christina, asking him to hurry to the ball that night. Vargas, who fancies himself Christina's suitor, impetuously delegates his command and takes off for Hermosillo. That night, as the mule train enters the town's portal, Catlow's men, hidden in the overhead beams, lasso the mule train guards one by one, then knock them out. When Vargas arrives at the ball babbling about Christina's message, Ben realizes he has been set up and rushes to the town square, where he spots Catlow's men and fires a warning shot to alert the officers attending the ball. After capturing Ben, Catlow leaves town with the mule train, instructing Rosita to stay behind and guard the marshal. To avoid the oncoming army, Catlow decides to cross the treacherous desert called "Hell with the fire out" because of its unremitting heat. Rosita, furious at Catlow for deserting her, imprisons Ben at her father's house, but he soon escapes and follows Catlow into the desert. As they make their way through the desert, Rio, an insolent member of the gang, challenges Catlow's authority and demands they turn around and head for Texas. Catlow, notified by his Indian guide Chaco that hostile Tonkawa Indians are in the area, insists that they stick together and threatens to kill anyone who tries to leave, prompting Rio to back down. Ben reaches the gang just in time to witness the Indians attack, after which they take refuge in the ruins of a deserted pueblo. Spotting Rosita and a gang of Mexican thugs she has hired to ambush Catlow hiding in the ruins, Ben fires a shot to alert his friend to the danger, then joins in the fray to overpower Rosita and her gang. That night, as they exhaust their last supplies of water, Ben informs Catlow that he intends to return the gold to its rightful owner, the U.S. government. As the others sleep, Rio slips Rosita a knife so that she can cut her bonds, then confiscates all the guns in camp. The next morning, when Rio and two others ride away with the gold, Chaco fells Rio with an arrow. As Miller watches from the hills, the Indians rally to attack the defenseless men huddled in the ruins. Suddenly, the Indians spot the approaching Mexican army and flee. After Ben arrests Catlow, they return to Hermosillo to await the arrival of the stage to take Catlow to trial. When the stage door opens, Christina is seated inside, ready to accompany Ben. Just then, Miller appears, holding a Mexican soldier hostage, orders everyone to drop their guns. After revealing that his vocal chords have slashed by the broken water jug, Miller fires, wounding Ben. Grabbing Ben's gun, Catlow kills Miller, then removes Ben's badge and pins it on himself. As Christina holds the wounded Ben, Catlow grins and appoints himself deputy, promising to bring the robbers to justice.