6. The Enterprise Incident
In one of the very few fine moments of Trek's third season (and I mean very, very, very few), Captain Kirk deliberately crosses the Neutral Zone without provocation in an attempt to steal a Romulan cloaking device. When a fleet of warbirds intercept the Enterprise, Spock denounces the Captain as insane and Kirk is charged with espionage. While in holding, Kirk lunges at Spock who then proceeds to kill him in self defense with the signature Vulcan "death grip," and the Romulans allow Kirk's body to be returned to the Enterprise (ever hear of suicide by cop? Suicide by Spock?) while Spock stays behind and the Romulan commander attempts to seduce him to the dark side (wait... wrong franchise again, sorry, but still she does try). Little do the Romulans know that this has all been a ploy by the Enterprise crew to board their ship and steal their cloaking device. Kirk returns to the Romulan vessel, surgically altered to appear a Romulan, and manages to steal the cloaking device. As the Romulan commander plans to execute Spock in retaliation, the two are beamed aboard the Enterprise, the commander a political prisoner, and before the Romulans can attack, Scotty manages to activate the cloak and retreat to Federation space.
5. Balance Of Terror
No, actually, that's not Sarek (Mark Lenard) up there. Lenard began on Star Trek as Kirk's Romulan adversary, the first Romulan ever seen by humans, despite a large scale war between them a century prior. The Enterprise is sent to investigate the destruction of several Earth outposts near the Neutral Zone, a demilitarized area of space similar to Earth's 38th Parallel, established between Federation and Romulan space that I promise newbies to the franchise will hear about until they're deaf in the ear from here on in. The attacker is a sole Romulan warbird exploiting Federation weaknesses, possibly to start a war. After a particularly interesting game of cat and mouse along the edge of the Neutral Zone, the Enterprise manages to cripple the Romulan ship, but the Romulan commander manages to activate the self destruct sequence to prevent Romulan technology from falling into the hands of the Federation. Before he goes to his death, however, the commander acknowledges Kirk's prowess in the hunt and delivers one of the more famous lines of the series, "n another reality, I could have called you friend."