The Survivor
Kirk discovers top trader and philanthropist Carter Winston five years after his disappearance, and takes him aboard. But with the ship ordered into the Neutral Zone, his identity is in question.
It's pretty obvious that the "survivor" isn't really going to be Winston. (Apparently one can only generate independent wealth in the 23rd century through trade, and then encouraged to put it back into the public sphere.) We know he's going to take advantage of Kirk's hospitality. Yet a shape-shifting alien who can become objects as well as people is something unseen before, and would have been hard to locate had he not wanted to be found. His turning into a deflector shield is a stretch, since he can only assume the shapes of things the same mass. (To my understanding, the deflectors are pure energy.) A good talent for a spy! The Vendorian seems to retain some memories of Carter, since he knew him, but saying he assumes anyone's traits and memories after a while is silly. Anne Nored is the most deluded ditz since Lt. McGyvers in Space Seed; she's only lucky that the Vendorian isn't evil. Kirk is a little quick to let him off, but meh. A pretty routine mission with some leaps in logic.
Spock Saves the Day: Spock suspects Kirk and McCoy might be acting oddly at different points, but is generally unhelpful.
Oops: That Spock doesn't see the connection between Winston and the Vendorian is most perplexing; the writing's again to blame.
Developments: Spock knows McCoy well enough to realize he wouldn't doubt his work, at least not in front of the Vulcan, and the identity switch is realized. The banter about the table is cute, but why isn't McCoy familiar with his workspace? If we were writing Bones' developments, he'd get an Oops too.