Guest starring former Miss America Lee Meriwether as a strange alien chick, this joyless mystery goes in circles (much like the third season) while she hunts down the Enterprise crew on a planet and simultaneously disrupts the ship.
Basically a sci fi ghost story, it avoids being blatantly bad like "And the Children Shall Lead" by offering a unique sort of charm. The alien woman herself is suitably creepy, appearing and disappearing with the look of an old time TV image when the set is turned on and off while a haunting musical stinger lends accompaniment. Unfortunately, she doesn't really have anything to say except "I come for you", and her scenes remain redundant until the big reveal at the end where all is explained.
The main cast itself is split, with Kirk, Bones, Sulu, and an extra down on a planet (one of whom dies to establish the danger, though I won't give away who), and Spock and the rest on the ship, which ends up rigged to destruct, establishing a countdown clock. In the hands of former Star Trek producer John Meredyth Lucas, all the principals stay within character, but with too little story to work with, he exaggerates their personalities to supply filler. Kirk is in such a Kirk-mode, he's obnoxious, treating his officers like they're third graders on a field trip. Spock is in such a jerk-mode, no one can say anything without getting a smart aleck reply. (Heck, Uhura asks him a question about odds, and Spock says "Lieutenant, we are not engaged in as if he doesn't spend the first two seasons telling everyone the odds for everything down to two decimal points. Screw you, Mr. Spock!)
In the end, . Fontana was so unhappy with the teleplay, she combined the first names of her brothers into a pseudonym for her story credit. (She needn't have worried; no one remembers the episode anyway).
Meriwether, who won the Miss America crown in 1955 as Miss California, would go on to better things as the secretary/daughter-in law in Barnaby Jones, a hit TV show in the 1970s.
Like the episode itself, there's not much of note here, just an upgraded starship and planet (replacing planet footage borrowed from Operation: Annhililate).