Texas, October 1873
Colonel Mackenzie, the commander of the 4th Cavalry Regiment at Fort Clark, Texas in 1873, receives secret order from President U.S. Grant and General Phil Sheridan to stop Mexican bandits from crossing the Rio Grande River into the U.S. or from returning to Mexico.
The settlers depend on the protection of the army who is absolutely trusted by them. Under Colonel McKenzie’s command his men patrol the area and buy horses and food from the settlers. A group of soldiers are ready to finish a deal with a settler. When the settler sees the signed payment he discovers a forgery, it is not McKenzie’s signature. Now they shoot him and take the horses and food with them. In his office McKenzie listens to a farmer, Mr. Benson, who accuses him of inefficiency. Several settlers have been killed by soldiers by now. McKenzie tries to convince the man that a uniform does not make a criminal a soldier. Benson is not convinced. All he knows is that many of his friends and families have been killed by men in uniform. He informs McKenzie that the settlers will shoot on any soldier approaching the farms.
Seeing that patrolling the area will be impossible under the condition, McKenzie takes his men to search the surroundings for the disguised killers. They succeed only in finding more civilians ready to shoot any soldiers. Because the settlers cannot detect whether a soldier or a killer is approaching the soldiers are in danger themselves. McKenzie draws the pattern of places where attacks have been done on a map and concludes that the gang operates from a place across the river: Prieto in Mexico. Now he thinks of Amos Nolen, a scout, and poses as the man.
In a salon in Mexico Rita approaches him and finds out that he is a scout, looking for work. Soon a man tries to push him away from her. He gets knocked down by McKenzie/Nolen. When he returns to the table a young man is sitting there. „You want to be next?“ He asks the man. „No, thanks,“ the young man says. „But if you can handle yourself like that, you might find some work around here.“
McKenzie clearly states that he’ll tell by himself when he needs any help and leaves. The young man, Anders, confirms with is friends, who are not as sure as he that McKenzie/Nolen really is a scout. They follow him to make sure.
Wondering whether he is being watched McKenzie is cautious while riding to his secret rendezvous with Lieutenant Mark Summers at Devil Horn Fort and makes a plan. Hiding in the bushes they witness him approaching the soldier saying, „Don’t shoot!“ (Because he could not risk a moment of recognition) McKenzie then knocks his Lieutenant down and robs him. Anders and the other man are sure: He’d kill his own grandmother for some dollar. McKenzie is sure that the killers would go for something more than anything other: A wagon load of army uniforms. He instructs Mark to train the best shooting soldiers to accompany the wagon.
Having arranged for wagons transporting hidden cavalry men McKenzie/Nolen sells the information to the gang. Their reaction is clear. „Why are you more interested in uniforms than in guns and ammunition?“ he asks Anders. „You’ll see,“ is all he gets. They take him along not to tell them the way but to ride along with them. He had not expected that. He is given a uniform to ride with them as a soldier. He remembers his own orders he gave to the real soldiers: Shoot the killers.
While fire is opened on the false cavalry men from the wagon McKenzie speeds up and shoots his fellow riders from the front. He is recognized by the soldiers and survives. Not so the false cavalry men. They are all shot.