Inspired by the 1931 Thorne Smith novel, Turnabout (in which a husband and wife wake up in opposite bodies), this "body snatcher" episode is infamous for its sexism and famous for being the last episode of TOS.
Written as simply another episode (and shot before the series was cancelled), the plot itself is somewhat of an embarrassment to Star Trek fans: with Starfleet only allowing men to be starship captains, one of them irrational women-people takes over Kirk's body and tries to run his ship.
The truth, of course, is that TOS is filled with sexist ideas, partly because of the prevailing attitudes at time it was made, and partly because of the specific producers and writers it employed. Yet some episodes, like "Wolf in the Fold", manage to cross the line while still remaining beloved, whereas others - most notably "Turnabout Intruder" - tend to be ostracized. And that's a shame, because it's actually a decent little episode with some fun highlights.
The ship-based story is basically a vehicle for William Shatner to play another part, and he's fully believable as a woman in a man's body even if he does play it over the top. (It's hilarious to see imposter-Kirk filing his nails while idly chatting with Shatner, along with the writer and the director, could perhaps be criticized for creating a stereotypical 1960s female character, babbling on like an airhead, but you can't fault the actor's commitment to throw himself into the part, adopting completely new postures and a new way of speaking.
And yet the real treat doesn't kick in until about halfway into the episode when Sandra Smith begins playing Captain Kirk. With the audience so much more familiar with him than the guest part, it's a greater acting challenge, but Smith nails it, capturing the essence of the captain and leaving no doubt as to her character's true identity. In fact, the real drama in the episode lies in Kirk's uphill attempt to win back his officers, his ship, and his body, and it's well presented. When we see Shatner's female character checking on Kirk only realize that Kirk has gained a powerful ally, Smith shoots the flustered intruder a Kirk glare as if to say, "Your move"
But despite some gratifying victories for the Captain over the bully, the climax itself is poorly designed, appearing out of nowhere with little setup. TOS's last episode suddenly solves its issue and quickly ends, leaving us with its last words: "If only"
If "The Doomsday Machine" represents the holy grail for this sort of project, "Turnabout Intruder" is an old shot glass. Or a thimble. That is to say that from an effects standpoint, there's not much to it. With the conflict almost completely confined to the ship's interiors, very few exterior shots of the Enterprise are shown.
CBS Digital does, however, get to replace a planet (originally just a reuse of the "Operation: Annihilate!" sphere) and sends the Enterprise off into the M45 Pleiades star cluster for the final shot.
Did you know? This episode was scheduled to air March 28, 1969 but was preempted by coverage of Dwight Eisenhower's death. It finally aired two months later to kick off Star Trek's summer season reruns in a new timeslot.