This is another of those episodes where the Romulans are flying Klingon warships for no readily apparent reason. Rather than deal with that, it was just easier not to draw them at all!

And yeah, Lieutenant M'Ress. Because the one thing Star Trek was missing up to this point was catgirls.

And double yeah, introduced in the same episode as tentacle-love. This series really was ahead of its time for children's animation.

Transcript

1
Captain's log, Stardate 5143.3. We've rescued Carter Winston, a philanthropist missing for 5 years.
Kirk: Your fiancee is on my crew.
Carter: Anne, I've changed. I can't marry you.
Anne: <sob>
2
{bridge}
Kirk: Set course into the Romulan Neutral Zone!
Sulu: Er, Mr Spock, have we set up protocols to check if an alien is impersonating the captain again?
Spock: Not yet, Mr Sulu.
Sulu: Sigh.
3
Kirk: {to Anne} Something is posing as your former lover? Now when has that ever happened before?
McCoy: Nancy Crater.
Chapel: Roger Corby.
4
Caption: First appearance of Lt. M'Ress!
M'Ress: Romulan warships, captain. Purrrr.
5
Spock: Carter is a Vendorian shapeshifter, spying for the Romulans.
Vendorian/Carter: I tended the dying Carter and absorbed his personality. I will change sides and help you escape!
6
Vendorian/Carter: Carter loved you, as do I now. Anne, this is what I am. Can you love this?
Anne: Hmmm... tentacles. I could get used to it...
Caption: Plot thing that actually happens