|You know it makes sense|
"Spock's Brain" (TOS) is often held to be the worst episode in the original series. But I would argue that it is not without some merit. And in any case it is more watchable and enjoyable than many "better" episodes.
The Enterprise is approached by a strange ship which has "ion power"—in the episode this apparently means an extraordinarily powerful source of energy. A woman beams over and causes them all to collapse. Cue titles. Next, McCoy calls Kirk to come to sick bay to see Spock. He looks dead, but McCoy reveals the awful truth: "His brain is gone!" McCoy can keep Spock's body alive for a limited time, so the Enterprise sets off in pursuit. They lose the ship when it enters the Sigma Draconis system, and Kirk invites recommendations on which planet to choose, which produces a rather nice scene. On the chosen planet it is an ice age, and there are men but no women. They go underground and find a high-tech world of women (with some male servants), including the woman they saw on the ship (Kara), but she seems to have no memory of this. "Brain and brain! What is brain?" she cries in frustration at their questions. It turns out that Spock's brain was taken to be the central processor—"controller"—of their computer. Overcoming resistance from the women, Kirk and the others recover the brain and return it to Spock, whose body they have brought with him. It has a remote control device and ticks when it moves.
It seems that this world developed from arrangements made by a more advanced civilization when faced with an ice age. There seems to have been some provision for the decay of knowledge, since there is a "Teacher" machine which temporarily gives the old knowledge to the leader—this is how she was able to pilot the ship and remove the brain. (McCoy uses this to gain the knowledge to return the brain.) Kirk tells them that without a Controller they will have to move to the surface, and the women and men will "control together". The Federation will give initial help. (This is one of those TOS episodes where the Prime Directive doesn't seem to be very important.)
It has to be said that a lot of the appeal is the appeal of "so bad it's good". It is memorable both in scenes—Spock's body, dressed for some reason in overalls, walking along under remote control, which could have been creepy but in fact is just bizarre—and in marvellous lines such as "His brain is gone!" But there is more to it.
There is definitely a "Planet of the Scantily Dressed Women" vibe here, but the accusation, sometimes made, that the portrayal of the society itself is sexist seems debatable if it's based on the women's childlike nature. The women aren't very clever, but the men, who live on top as cavemen, are even less clever. The situation whereby the men are controlled by a mixture of pain and reward by dominant women might be another question, though on the other hand you might see the theme as kinky rather than sexist.
The two-level society has echoes of The Time Machine, but here the Eloi (women) are below, and in charge, and the Moorlocks (men) are on the surface. Spock ends the episode lecturing the others about what he has learnt, and explains that originally the women went below for shelter, presumably a sort of "women and children first" thing. It became a "retrograde civilization". The women, in controlling the men, are "the givers of pain and delight", though reference is mainly to the former, with the women carrying devices to zap the men with pain. "No one wants to find them!" protests one of the cavemen when Kirk asks if he can be taken to the Others.
Anyway, this is an episode that you can pull out whenever you need something undemanding, mildly interesting, somewhat silly, and very watchable.