TAS "The Survivor" by James Schmerer
This is one I have to see I may never have seen. It looked completely unfamiliar to me.
Patrolling near the Neutral Zone, the Enterprise finds a small ship with Carter Winston (Ted Knight!) inside. He's one of those rich adventurer/philanthropist and he's been missing for five years. Winston's fiancee, Lieutenant Anne Nored, is a security officer aboard the Enterprise. She's thrilled to see him, but he breaks off their engagement without explanation.
We soon see it's not Carter Wilson, but an alien shapeshifter who has taken his form. The Vendorian knocks Kirk out, takes his form, and orders the ship into the Neutral Zone. Romulans warbirds are there to meet them. Kirk wakes up, is told where they are and doesn't remember ordering it, so he goes to see McCoy. But the Vendorian takes McCoy's form to fool them. Spock figures out he's a fake when "McCoy" admits to a mistake (which made me laugh a lot). A new exam table shows up in sickbay and Kirk and Spock aren't fooled and force it to take it's true form (a form that would not have working in live action with the budget available). The Vendorian was hired by the Romulans to lure the Enterprise into the NZ.
As Our Heroes are about to be blown up, the Vendorian takes the form of a deflector shield (which it had sabotaged earlier) and saves them. It explains that it had been with Winston when he died and preserved his memories and personality, gradually taking them as its own, thus the change of heart. Lt. Nored volunteers to guard it because it's similar enough to Winston that she cares for it.
Earlier in the episode, Nored had trouble taking action against the Vendorian because it looked like Winston. That's a bit like the salt vampire looking like McCoy's old lover in The Man Trap. However, Nored makes up for it later and I liked seeing a female security officer. It's a tight episode, but the Vendorian's turnaround is a little quick. I consider this an ok episode, mostly because of the time constraints. Ted Knight was, as always, terrific.