An undercover mission to steal a Romulan cloaking device takes the Enterprise into the Romulan neutral zone, upon which Kirk and Spock beam over to a Romulan ship under the guise of Kirk being insane and commanding the Enterprise into the neutral zone on his own personal accord. Subsequently, Kirk is imprisoned while Spock catches the interest of the Romulan commander (Joanne Linville).
Given the broadcast sequence, one wonders how this episode can even be the same series that supplied "Spock's Brain," but never mind. "The Enterprise Incident" is an exceptionally skillfully executed spy mission that manages to keep the audience guessing every bit as much as the enemy. Featuring a tight, compelling plot with adept twists and turns and logical action, the story also pushes Spock's character into new territory.
Spock's manipulative liaison with the Romulan commander benefits from an intriguing eroticism that exists outside the human expectations and instead shows a Vulcan form of subdued, cautious, and very mind-oriented sexuality. The fact that Spock got more than he bargained for brings forth a touch of fascinating sentiment where the emotion behind the encounter is evident but never spelled out in performance. All in all, one of the series' best outings.