Just how much treachery and deception can fit into a single hour of Trek? That seems to be the most useful question to ask of "Friday's Child," an episode full of double-crosses and marginally clever traps and tricks.
The plot involves Kirk, Spock, and McCoy (and a soon-to-be-dead red-shirt) beaming down to Capella IV to negotiate a deal for minerals with the warlike tribes living there. The Klingons, however, are also there to negotiate, and the treachery between the Klingons and the Capellas—and even a struggle within the Cappella tribes' own hierarchy—quickly becomes a free-for-all. The landing party escapes imprisonment, but not before the show begins suffering from the fact it seems D.C. Fontana kept randomly inserting "[FIGHT SCENE]" into the script. Meanwhile on the Enterprise, Scotty chases a distress signal from a freighter. The signal turns out to be a Klingon forgery intended to lure the Enterprise away from Capella so the Klingons can thwart the landing party and plunder the minerals, but Scotty discovers the trick in time.
The editing technique with the cross-cutting storylines is rather annoying, switching back and forth so frequently that it's hard to care much about either storyline. The episode benefits from some great lines and sarcastic looks from Mr. Spock, and also some chemistry between McCoy and the pregnant Eleen (Julie Newmar), but it's not enough to save an hour so lacking in direction that it becomes a disjointed sum of its parts. What a shame to waste such effective outdoor photography.