Gideon, the Good - S12.E6

On the trail, Joe witnesses a woman kill a man, but the woman rides away before he can positively identify her. He rides into the nearest town, Black River and reports the crime to Sheriff Gideon Yates, and the two ride out to find clues. They find a handkerchief embroidered with the letter "L". Sheriff Yates knows who the killer is, his wife Lydia. She married him before she got a legal divorce from her first husband, Loomis, and killed him to silence him.

Gideon tries to coax Joe out of town, but he recognizes Lydia's picture in a photographer's window. When Joe refuses to leave, Gideon tries to shoot him down in cold blood and orders a manhunt against him. Joe's only hope is a Mexican stable boy, who saw Gideon shoot him, and ultimately Joe and Gideon have one of the most memorable confrontations in the series' history.