Clearly influenced by Mission: Impossible, this is Star Trek at it’s “what the hell?!?” best. The first time I saw this episode, I was stunned, baffled and wondering if this were somehow the final episode of the show–this despite knowing the series would later live on in the movies.
Kirk is acting a bit irrationally–snapping at crew members, ordering the ship across the Nuetral Zone, etc. It’s interesting that a lot of Trek episodes that involve captains other than Kirk show those captains going mad or the power of command going to their head. So, that Kirk could slip into this is not that far of a stretch based on what we’ve seen.
Before you know it, the ship is surrounded by three Romulan war-birds (the Romulans begin using Klingon ship design to save the budget) and Kirk and Spock beam on-board the Romulan flag-ship. they meet the female Romulan commander who takes a liking to Spock and it appears Spock takes a liking to her. Spock appears to betray Kirk and the crew, leading to the infamous Vulcan death grip (there is no such thing) being used on Kirk.
It turns out this is all a cloak and dagger mission by Starfleet. Kirk and Spock are in on it, but on one else is…that way if it fails, Kirk is hung out to dry and no one in Starfleet suffers. They are there to steal the Romulan cloaking device, which Kirk does by disguising himself as a Romulan. Spock, meanwhile, distracts the female Romulan commander by apparently seducing her–all while she promises him high office and rankings in the Romulan fleet should he do so.
As I said before, the first time you see this one, it’s a head scratcher. Kirk has snapped, Spock is betraying the crew and McCoy is declaring Kirk dead. The first 30 minutes are superb, setting up the plot within plots to get the Romulan cloaking device. Outside of Khan, the female commander is one of the most fascinating of the original series villians, as evidenced by at least four returns to the universe in Trek novels. (Including the infamous “Killing Time”). The Mission: Impossible element is great, the character work is solid and the scene of the Enterprise surrounded by three ships is one of the icons of Star Trek.
All this from the pen of D.C. Fontana who script-edited and wrote a lot of the best episodes of the original series.