Originally Aired: December 13, 1959

Gunsmoke #401, "Don Mateo," Matt Dillon's past comes calling when Don Esteban, an old friend from his days riding the Mexican border, arrives in Dodge City looking for him. The reunion at the Long Branch starts with warmth and nostalgia as the two men reminisce about their dangerous adventures together, hunting outlaws in territory where they made their own law. But Esteban hasn't come just to visit. He's tracking a man named Rallo who has wronged his Maria, and he wants Matt to ride with him like the old days.

Matt faces an impossible choice between loyalty to his friend and his duty as a U.S. Marshal. When he refuses to join the hunt and warns Esteban that he'll have to come after him if he kills Rallo, the Mexican sadly observes that his old partner no longer has "the enjoyment." The tension escalates when Chester brings word that Doc is treating a wounded dirt farmer, shot by a rider in Mexican outfit. Matt must now confront whether his old friend has crossed the line from the borderlands justice they once shared to cold-blooded murder.