Bonanza S03E23 - The Guilty

Tucson gunman, Jack Groat, swore to kill Sheriff Lem Partridge for putting him in prison after a bullet from Groat's gun during a drunken street brawl accidentally killed Sheriff Partridge's wife. Now, 10 years later and fresh out of prison, Groat has tracked retired Lem Partridge to Virginia City and is soon holding Lem's son, Jimmy, and good friend Ben Cartwright hostage. But things go bad and Ben must soon explain to Lem - and try to convince himself - that there was nothing he could have done that day to stop Groat from shooting Jimmy in the back.