The Day of the Tin Trumpet - S1.E20

Seeing an old derelict being harassed by thugs, Doc and Jaimie invite the man to join them on the wagon train. The old codger interests Jaimie and the other kids with his stories about past adventures on the frontier. But he doesn't tell anyone that he recognizes the "U.S. Marshal" who stops by with his wounded prisoner as a killer outlaw, because the outlaw knows a secret about the old man that he'd rather not have revealed as well.