The Enterprise is sent to an uncharted region of space known as the Delta Triangle, where hundreds of ships have disappeared over the last few hundred years. (Apparently nobody thought it was a bad idea to send another single ship without any kind of backup to this venture.) They run into Klingons, as happens on occasion, but when they return fire the Klothos disappears, despite having clearly deflected their shot, and leaving no flotsam.
When the other Klingons don't believe Kirk's explanation, he flies the Enterprise directly into the spot the Klingon ship disappeared from and winds up in a starless void full of stranded ships—including the Klothos. Attempting to reignite the battle has Kirk and Kor transported to one of the stranded vessels to face a council of various species, who have banded together to form a pacifistic society they've dubbed "Elysia." They warn Kirk and Kor that violence is forbidden and attempting to escape is useless, but agree not to prevent them from trying.
Kor agrees to work with Kirk to try and escape the Triangle. Spock, "overcome with the moment" of historic cooperation between two adversaries, starts acting very chummy towards the Klingons, draping his arms over their shoulders and freaking the hell out of McCoy until he reveals that he was doing a low-grade mind meld... and that they're planning to sabotage the ship. Despite being on their guard, the crew gets drawn into a Batman Gambit by Kor, who is able to covertly plant an Advil gel-cap bomb in the engine until a psychic Elysian figures it out and calls them. Spock throws the pill out of the garbage chute as the Enterprise and Klothos make a successful escape.
Tropes:
- Batman Gambit: Kor has one of his men start a fight during an Elysian reception, which provides a distraction so that his saboteurs can plant the bomb. He's counting on Kirk to advocate for the Klingon ship to not be impounded, since they need both to escape, and the Elysians to agree.
- Continuity Nod: One of the Elysian council members is a Phylosian ("The Infinite Vulcan").
- Derelict Graveyard: Kirk flies the Enterprise into a space anomaly that contains dozens of starships, recently lost to centuries old. Rather than being lifeless wrecks, however, their crews are alive and well.
- Fascinating Eyebrow: When Kirk vanishes, the camera cuts to Spock's face, sloooooowly zooms in, and then with a dramatic music cue—his eyebrows contract.
- Green-Skinned Space Babe: The Elysian lawgiver is an Orion woman in a bikini.
- Karma Houdini: Kor suffers no repercussions for his treachery, which he then compounds by claiming he got out of the Delta Triangle solely by his own ingenuity. In the Novelization, it is revealed that Kor believed the Enterprise destroyed and broadcasted his 'triumph' to the entire Klingon command, meaning at the very least he's in for heavy duty embarassment when they figure out the truth.
- Locked in a Room: Kirk is trapped in an anomaly with his old enemy, Kor, and proposes a cooperative venture to escape. Kor uses it as an opportunity to destroy the Enterprise.
- Negative Space Wedgie: The disappearances in the Delta Triangle are caused by two timeframes colliding.
- O.O.C. Is Serious Business: Spock gets very touchy-feely with the Klingons, claiming to be "overcome" with the spirit of cooperation. This (naturally) freaks out McCoy and Kirk who have some serious doubts about his sanity. Especially worrying since it is his computations they're basing their very risky escape attempt on. Turns out he's covertly doing his Touch Telepathy on them.
- Perfect Pacifist People: Elysia. After being trapped for so long, all the disparate ships have formed a cooperative society and have very strict punishments against any violence.
- Punny Name: What does the Greek letter delta look like? A triangle.
- Recycled Animation: Commander Kuri is reused footage of Koloth from "More Tribbles, More Troubles." Also, Sulu is shown sitting upright in his chair in the standard "whole bridge" ceiling shot moments after fainting and falling over.
- Space Is an Ocean: One reviewer commented that they should have called the anomaly the Delta Pyramid rather than a triangle.
- Stealing the Credit: Kor sends a transmission to Qo'onos claiming sole credit for the escape. Kirk lets it slide since he's just happy to be out.
- What Happened to the Mouse?: With Kirk and Kor's efforts proving that escape is feasible, what happens to the Elysians?
- Year Outside, Hour Inside: Something like this applies to the Triangle—time passes, but has no effect. The Elysian council claim to be centuries old.
