Starring William Shatner, Leonard Nimoy
Guest Stars: Jeanne Bal, Alfred Ryder, DeForest Kelley, Grace Lee Whitney, George Takei
Directed by Marc Daniels
(actor & director credits courtesy IMDB.com)
The Enterprise visits a barren planet to give a geologist and his wife, an old flame of McCoy's, medical checkups, but the lady is actually a murdering monster in disguise.
The first episode of the series to be aired on TV (although the sixth filmed), I've always enjoyed this one, with Daniels and crew employing some clever stylistic touches to track the monster aboard ship as it assumes many disguises, including having the actors impersonating the salt-hungry creature by sucking on their knuckle, and accompanying its transformations with a musical flourish. The creature makeup is quite memorable, and the screenplay bats around some worthy ideas, comparing the creature as the last of its kind with endangered species on our contemporary Earth.