The Restless Breed (1957) on Netflix

Plot summary

Mitch Baker, a quick-tempered young lawyer, is called in by the Secret Service and told that his father, one of its agents, was murdered in Mission, Texas, betrayed to Newton, who runs guns across the border to Emperor Maximilian I of Mexico. Offered his father's badge, Mitch takes only the pistol and rides to Mission to settle the score, posing as a gunslinger. In that town, previous sheriffs have been murdered soon after taking office, and Simmons, a self-proclaimed preacher, keeps a shelter for children of mixed Indian and American parentage whom neither side wants. The oldest, Angelita, hopes to dance in the local saloon and is fascinated by the stranger.