The DVD background blurb likens this episode to "The Ox-Bow incident", which I have not seen, although I've heard of it.
Paladin is peacefully ambling along, presumably to or from a "case", when he is suddenly ambushed and hauled off (under protest) to a nice little campsite with all the amenities: fire, food, shade...a noose.
He faced with an angry rancher, who throws the statement "She's dead!" in Paladin's face, which only confuses him more. He's not the only one; a young "singing cowboy" is already present (and having only seen James Best as "Roscoe P. Coltrane" I was startled at how handsome he is) and they are quickly joined by a third party, a gun salesman who, oddly enough, has never personally used his merchandise.
They soon learn that the element they have in common is their black attire: the rancher's lovely (and very young) wife had been caught the night before with a stranger, and all her husband had seen of him was his black shirt. The outraged husband promptly set his men to tracking down all black-garmented men in the vicinity. (Doesn't seem to have occurred to him that the man might have changed clothes.) The rancher being extremely wealthy, and his wife from a high-society Mexican family, all three men admit to having some knowledge of the couple. The rancher initially accuses one of them of having killed his wife. This changes to her having been accidently killed when she stepped into the line of fire when her husband fired at the fleeing man. It doesn't take Paladin long to point out the flaws in this story, and the truth comes out: the rancher deliberately shot his wife when she refused to tell him the name of her visitor. He refuses to take responsibity for her death, and intends to kill the man she had been seeing...once he can figure out who it is. His idea is to leave the three men talking around it until the truth comes out.
No one wants to admit anything, of course, with that noose hanging overhead. When it becomes clear that the rancher will kill all three of them to ensure getting the "guilty" party, Paladin gets the idea of having one of them "confess". The other two will then circle back and rescue him before he can be hanged. The gun salesman gets the short straw, but the idea falls flat when he refuses to confess to something he didn't do. (And perhaps he was worried that the other two would just high-tail it out of there and leave him to die.) Paladin, exasperated, confesses himself, only to find that the other two will not be allowed to leave until they've witnessed the hanging. The singing cowboy offers to sing him a eulogy, then clobbers the nearest henchman with his guitar. (Hmmm...a genuine use of the "blunt instrument".) This, of course, kicks off a gun battle. The gun salesman seems remarkably adept at handling a weapon he claims never to have used before; one flaw in an excellent episode. The ending is grim, but fitting. Paladin, having cleared the field of battle, sends everyone on their way, and resumes his own interrupted journey.