Star Trek: The Enterprise Incident

On stardate 5027.3, Captain James T. Kirk takes the USS Enterprise, without authorization, into the Neutral Zone between Federation and Romulan space. Three Romulan warbirds decloak and intercept the ship and Kirk is given an order to surrender. Kirk responds by threatening to destroy the Enterprise if the Romulans attempt a boarding. He is then invited, along with Mr. Spock to a parley aboard the lead Romulan vessel. Kirk accepts on condition that the Romulans simultaneously transport two of their officers over as hostages.
Once aboard the Romulan ship, Kirk and Spock are taken before a female commander who demands an explanation for their intrusion into Romulan space. Kirk explains that instrument failure caused the ship to stray off course, but Spock claims the captain ordered entry into Romulan space as an initiative born of insanity. The Romulans lead a furious Kirk, charged with espionage and railing against the treachery of his First Officer, to the brig. The Romulan Commander then orders Mr. Scott to follow the Romulans back to their base but the combative Scott refuses.
In the Romulan brig, Kirk injures himself by lunging against the force field enclosing the cell door. Dr. McCoy is then summoned from the Enterprise to attend to him. With Spock in tow, the Romulan commander asks McCoy to confirm Spock's characterization of the Captain as being mentally incompetent and McCoy does so. After listening to the Romulan Commander order Spock to assume command of the Enterprise, Kirk mutters words of outrage and disgust, then lunges at Spock. Spock defends himself by using the "Vulcan death grip" – understood to be a variation on the Vulcan nerve pinch – on the Captain, who slumps to the floor. McCoy then declares him dead.
Alone with Spock in her quarters, the Romulan Commander continues her attempt to persuade him to her people's cause. She argues that humans show their prejudicial disregard of Vulcan talents and capabilities in failing to have placed him in command of a Starfleet ship, but that, should he switch allegiances, he will learn to enjoy the spiritual society of Romulans as her consort.
Back on the Enterprise, Kirk returns to life, emerging from a mere state of suspended animation brought on by Spock's "death grip", and orders McCoy to perform the plastic surgery necessary to give him Romulan features. With his features altered, Kirk borrows the uniform of one of the Romulan hostages and has Scotty transport him back to the Romulan vessel.
While the Romulan Commander is changing into more comfortable attire, Spock directs Kirk, via communicator, to the section of the Romulan ship where the cloaking device is located. From the bridge, Romulan Subcommander Tal discovers and tracks the signal. While Spock and the Romulan Commander commune with one another in a spiritualized erotic exploration of the other's hand and face, Tal interrupts and informs his superior of the alien transmission. Spock presents himself to the Romulan officers affirming Tal's report, but also that they are too late – Kirk has disengaged the cloaking device and returned with it to the Enterprise.
Spock takes advantage of the traditional Romulan right of statement before his conviction and eventual execution to stall for time. Simultaneously, Kirk assumes command of the Enterprise as Scotty attempts to sync the the Romulan cloaking device technology to the Enterprise deflectors. Ensign Chekov tries to distinguish between Vulcan and Romulan life signatures so that Spock can be transported back to the Enterprise. He eventually acquires a fix on Spock and begins to beam him back to the Enterprise. As Spock dematerializes, the Romulan Commander rushes to embrace him and she is beamed over with him. They materialize on the bridge of the Enterprise where Kirk gives the order to return to Federation space. The pursuing Romulans are ready to fire upon them as Scotty activates the cloak and the Enterprise vanishes before their eyes.
Kirk orders the ship to the nearest starbase and gallantly invites the Romulan commander to accept Mr. Spock as her escort to her new quarters. Alone with Spock in the turbolift, the Romulan acknowledges defeat and expresses her bitter disappointment at Spock's betrayal. Spock avers that, although his loyalty is to the Federation, she underestimates herself considerably if she believes he was not tempted.
Later on the bridge, Spock overhears McCoy teasingly ask the Captain whether he wishes to return to sickbay for surgery, or whether he wishes to look like his First Officer for the rest of his life. Spock urges the Captain to go, since Romulan (and by implication, Vulcan) features on humans appear distasteful to him.