A woman steals Spock's brain for use as a utilities regulator on her home planet, leading Kirk and crew to go on a mission to retrieve it. Yes.
How or why she came about choosing Spock's brain is as unknown as why this episode was ever produced in the first place. Possibly the dumbest episode in the entire Trek canon, "Spock's Brain's" sole saving grace is the fact that it's so bad it's downright funny. The unintentional hilarity of this episode almost makes it worth experiencing, simply so you can shake your head and laugh in disbelief.
What on Earth was Gene Coon (entering this under his pen name) thinking? The plot is beyond hopeless and utterly nonsensical; the performances are beaming in from another galaxy; and the jokes fail to be funny while the (apparently) serious moments cause unrestrained laughter.
My snickering continued throughout the episode, occasionally peaking at the many moments when Kirk demands in desperation, "What have you done with Spock's brain?!" Before long, the very words "Spock's brain" become laughable. Perhaps even Marc Daniels couldn't take this remotely seriously, having seemed to direct it with all the cheesiness the story is worthy of. The epitome of bad science fiction.