When a landing party beams down to investigate a planet, a mysterious woman named Losira (Lee Meriwether), armed with a deadly touch, begins attacking several members of Kirk's crew, both on board the ship and on the planet surface. The problem is magnified when the Enterprise is hurled far away from the planet and its engines are sabotaged, causing a countdown to the ship's destruction.
"That Which Survives" is as close to nothing that you can have on the screen and still have some semblance of a Star Trek episode. The familiar two-tiered story structure does nothing here, failing on both counts. The landing party's lobotomized attempts to uncover the mystery of Losira have precisely zero urgency and thought put forward. Meanwhile, the technobabble-heavy Enterprise jeopardy plot is completely insipid; not one character on the ship seems to really believe that they're going to "blow up in 15 minutes."
And on top of the uninteresting nature of the story, we have to put up with one of the most irritating utilizations of Spock ever conceived. Spock's sarcasm is entertaining when wittily and subtly developed, but here his quip one-liners are so needless, pervasive, and annoying that I simply wanted to strangle him. (Just how many times can we listen to him snidely telling Scotty to forego emotionalism and get to work?) The finale uncovers a mystery that is not remotely worth the effort required to get there.