Has Captain Kirk (William Shatner) not only lost his ability to captain his ship but lost his mind? At episode's beginning, Captain Kirk is irritable, irrational, and nearly insufferable. And then he takes the Enterprise into the so-called "Neutral Zone", an area of the galaxy which is off-limits to Federation fleet ships under current treaty with the Romulans, the nemesis of the galaxy. The Neutral Zone acts as an interstellar buffer between the Federation and the Romulan Empire. Kirk violates the treaty and is immediately confronted by Romulan military starships.
Their commander is a beautiful but highly intelligent Romulan woman, simply called "Commander" (Joanne Linville). She is aware of the violation of the treaty and will not let the Enterprise return to Federation space without making a point. She desires to take the Enterprise and crew hostage, and to execute Captain Kirk as an example to other wayward starship captains. She then finds a strange ally in Mr. Spock (Leonard Nimoy) who, after beaming to the Romulan ship with Kirk, confirms that Captain Kirk is suffering from delusion and insanity. An unexpected subdued flirtation evolves between the Vulcan and the Romulan. Both Nimoy and Linville play their rolls perfectly, subtly engaging but never overt. Captain Kirk appears to become more infuriated when the Vulcan appears to have betrayed both him and the Federation.
This is one of the best episodes from the original Star Trek series of the 1960's. It exploits the rivalry of the Romulans and the Federation, and it has some of the best acting of William Shatner and Leonard Nimoy combined with a compelling and unpredictable storyline. Highest marks also for Joanne Linville as the Romulan Commander who never raises her voice, even when she condemns Captain Kirk to death.