In Arizona, the Sturges family owns a horse ranch. On the way to the market, their horses are stolen by masked outlaws who also kill the ranch hands. One cowpoke survives and sounds the alarm at the Sturges ranch. Owner Mike Sturges and his younger brother Roy, accompanied by their foreman Bobcat Bates go after the murderous horse thieves. Unfortunately, they will run into a gang of train robbers who wait in ambush for the next train carrying gold from the nearby mines. Bobcat is killed and brothers Mike and Roy shot and left for dead near the spot where the train is ambushed. The next day, the sheriff, his posse and Southern Pacific agents find Mike and Roy laying wounded at the scene of the train robbery. It's assumed they are members of the train robbing gang. Despite their pleas, the sheriff and his men beat Mike and Roy and arrest them. Later, they are sentenced to years of hard labor at the quarry belonging to Yuma Territorial Prison. In prison, the treatment of inmates is harsh. The sadistic guards' captain intentionally targets Mike and his frail brother Roy. With increasing doubts about Roy's chances of survival and Mike's chances at a pardon, it's decided to join a select group of inmates who are planning a prison break. Mike is dreaming of escaping in order to find the real train robbers and prove his innocence. He sorely misses his wife and ranch. But escaping Yuma Prison is no easy task and finding the train robbers will prove to be almost impossible since they are protected by a corrupt lawman who's on the take.