This episode has two -- count 'em, two -- surprise revelations at the end. I won't reveal them. Be cautious about reading other reviews.
Though I've poked merciless and well-deserved fun at "The Big Valley", I have to admit it got better as went along. (Which makes one wonder why there so many awful -- and I mean really awful -- episodes in the first two years.) This is an exceptionally good episode.
In retrospect, the court-martial of Nick Barkley and his commanding officer (Henry Jones) for the murder of civilians seems to be a comment on the My Lai massacre -- yet it was made a year prior.
Though the story itself is clever and entertaining, the main reason for watching is Henry Jones' performance. Jones is one of the all-time-great character actors. He's best-known for ironic/sardonic roles (the coroner in "Psycho", the handyman in "The Bad Seed"). Here he plays a straight dramatic role. His casting is spot-on, as a lesser actor wouldn't have been convincing.
One of the few "Big Valley"s actually worth watching.