High Plains Drifter (1973) on Netflix

A Stranger rides into in the dusty mining town of Lago, where the townspeople are living in the shadow of a dark secret. After a shootout leaves the town's hired-gun protectors dead, the town's leaders petition the Stranger to stay and protect them from three ruthless outlaws who are soon to be released from prison. The three have their sights set on returning to Lago to wreak havoc and take care of some unfinished business. A series of events soon has the townspeople questioning whether siding with the Stranger was a wise idea as they quickly learn the price that they each must pay for his services. As the outlaws make their way back into Lago, they discover that the town is not exactly as they had left it, and waiting in the shadows is the Stranger, ready to expose the town's secret and serve up his own brand of justice.