This tedious episode never should have been made. It's a good example of a "science fiction" story in which a routine non-sf scenario is given superficial sf trappings. (see C. S. Lewis's objections to this type of story in "on Science Fiction.") You can see the sf elements actually working against the story in that the killer is a 19-year-old girl who has been killing witnesses of her father's mass-murder, as a traveling company of actors goes from planet to planet. It would be easier to accept the premise if the company were earthbound and traveling from city to city.
It's creepy to have Kirk, who was an adult witness of Kodos's reign of terror, romancing his 19-year-old daughter, first of all because of the age difference. Anderson doesn't look 19, so that mitigates it a bit.
I can only guess that the script idea appealed to Roddenberry & Co because it would be different from a space opera or monster type of show; it wasn't about a strange disease (such as they used within two of the first dozen shows, "Naked Time" and "Miri"); it would please budget types because it wouldn't call for a lot of special effects, and so on.
The plot twist (that it's Kodos's daughter, not Kodos, who has killed seven of the nine surviving witnesses) is not well handled; only in the last few minutes do we have Kodos saying something about memory impairment, and only at the very end do we see that the daughter is a homicidal maniac.
Finally, this is one of the episodes in which cast members sing (Uhura sings "Beyond Antares"). Without exception these scenes always make me cringe inside.
Star Trek was occasionally pre-empted, and I feel like I'd rather watch one or other of the things that pre-empted it than to watch this one again.
