Interesting primarily for its guest appearances, Friday's Child is one of Joe Pevney and D. C. Fontana's more mediocre efforts. Among the guests is great musical and stage actress Julie Newmar, who is mainly known to TV audiences for having played Catwoman in the classic Batman TV show. Casting called for a number of very tall and beefy people, so many of the guest stars are over 6' and recognizable by sight if not by name.
The trinity (Kirk, Spock, McCoy + a soon-to-die redshirt) have beamed down to a planet inhabited by a very hierarchal, male-dominated culture whose rank system revolves around violence. Upon arrival, they find that a Klingon (only one?) has arrived before them. The Klingon has been propagandizing against the federation since his arrival, and has jeopardized the Enterprise's mission to obtain mineral rights. The redshirt makes matters worse by threatening the Klingon at first sight.
Although McCoy once lived on this planet and briefs the crew on some ethnographic details ahead of time, these preparations were not nearly enough, as the away team creates one blunder after another. Fontana did a nice job of thinking out the alien culture's intricacies, but unfortunately, the episode devolves into a somewhat unoriginal action adventure about mid-way through.
Cinematography and effects are very average for TOS, writing is OK, directing is well below Pevney's usual mark, and acting is fairly good. Look for a lot of amusing but hokey banter with Spock in this one, and a solid and interesting performance by Ms. Newmar.