Shari Lewis (the perky ventriloquist with Lambchop) wrote this dreary episode with the help of her husband for herself, though the producer (much to her ire) chose someone else to play Mira Romaine, the cute librarian who comes on board the Enterprise and has Scotty all over her while Kirk devotes long, poetic log entries to their romance. (If this was written today, Lewis could just post it on the internet as a fanfic). The story itself is a mix of science fiction and horror, like a cross between and "Where No Man Has Gone Before" and "Wolf in the Fold", even borrowing former's score to great effect.
Its fatal mistake, however, is that it's all about "the girl", as everyone calls her, and the show might as well have cast Lewis, because Jan Shutan is so abrasive and annoying it's hard to find any sympathy for her character. (Kirk sure That's a shame, because the episode has a few good moments as a horror story, and - like several other third season episodes - its aliens are creatively different. But in the end, people watch the show to see what happens to Kirk, Spock, and the other regulars, and no one cares about Mira, no one cares about the aliens, and everyone just wonders when Scotty will get back to his day job. (It's a good thing Lewis didn't quit hers).
Like "Day of the Dove", the original episode includes a mixture of live action and effects that can't be separated, but here CBS Digital does a good job of overlaying some enhancements. Meanwhile, the exterior shots are reinvented to better tell the story, with the best replacement being the library planet. (The original is just a red blob, being a reuse of Vulcan from "Amok Time", but the new is an amazingly detailed sphere featuring a visible complex). An impressive chart on the viewscreen, complete with a mobile representation of the aliens, is left as is.