Bonanza - Season 6 (1964-1965)

Season 6 was the first of three consecutive seasons that Bonanza was the #1 show in Prime Time Network television.

Episode 19
The Flannel Mouth Gun

(Adam is the only Cartwright in this episode)
A series of cattle rustling has the Cattle Association sending in a hired detective with an itchy trigger finger

aired - January 31st 1965
NBC