The USS Enterprise is on duty near the Romulan Zone border, and things are calm enough that Kirk can preside over a wedding between two crew members. An urgent call from an Outpost interrupts the wedding, and the ship discovers that a series of outposts have been destroyed by a new energy weapon. A lucky interception of a message from an unseen space ship allows Kirk and crew to find out who they are up against: The Romulans. Using a single cloaked ship firing the most lethal weapon ever witnessed. And The Enterprise is the only one who can stop them...
This episode contains the following tropes:
- Attack Pattern Alpha:Romulan Commander: Escape Maneuver One, quickly!
Stiles: Transverse pattern! All phasers fire!
- Better to Die than Be Killed: "Just one more duty to perform..."
- Blood Knight: Decius.
- The Chains of Commanding: Kirk reflects on this at one point with Bones.Kirk: I wish I were on a long sea voyage somewhere. Not too much deck tennis, no frantic dancing, and no responsibility. Why me? I look around that Bridge, and I see the men waiting for me to make the next move. And Bones, what if I'm wrong?
Bones: Captain, I—
Kirk: No, I don't really expect an answer.
Bones: But I've got one. Something I seldom say to a customer, Jim. In this galaxy, there's a mathematical probability of three million Earth-type planets. And in all of the universe, three million million galaxies like this. And in all of that, and perhaps more, only one of each of us. Don't destroy the one named Kirk.
- Combat Pragmatist: Kirk and the Romulan commander, both. As noted below the Romulan is prepared to use the body of his dead crew to fake their destruction, and Kirk learns pretty rapidly from his earlier mistakes in confronting the Romulans. This leads to them ultimately acknowledging each other as Worthy Opponents.
- Diving Save: During an attack by the Enterprise on the Romulan ship, the Centurion sees that the ceiling is about to fall on his friend the commander. He rushes forward and pushes the commander out of the way, and the ceiling falls on him instead.
- Due to the Dead: The Romulan commander orders the dead Centurion's body dumped into space along with a bunch of debris to make it seem that his ship has been destroyed — but he is clearly distressed about it, and asks his late friend to forgive him.
- Early Installment Weirdness:
- Scotty states that the Romulans' "power is simple impulse." This caused many people (including the writers of the Star Trek Encyclopedia) to assume that the Romulans only had Impulse engines and not Warp Drive. However, considering it would take decades for the Romulans to travel space without Faster-than-light travel, it would be nearly impossible to fight an interstellar war. Eventually, this was retconned by clearly showing that the Romulans have warp capabilities in Star Trek: Enterprise. Although Star Trek: The Next Generation DID establish that Romulan vessels were powered by artificial singularities as opposed to a warp core familiar to Starfleet. One of the EU novels, set in Captain April's era, explains this by having birds of prey capable only of sublight be deployed to their duty sectors by a warp-capable mothership. Impulse engines on Starfleet vessels are powered by fusion reactors. Knowing this and that a fusion-powered ship would have much shorter range than an antimatter-powered one, just like the Bird of Prey, it's probable that Romulan ships of the era were powered by fusion reactors and that Scott just meant that, and that artificial singularities (that would ensure pretty much unlimited range) were still to be developed.
- The Enterprise fires phasers in short bursts which detonate at a specified interval, in reference to depth charges. This could have easily been done by Photon Torpedoes had they been invented by the writers sooner.
- The Enterprise having a separate phaser control room where a crew fires the weapons. In later episodes, this task would be done remotely by Sulu from the helm, without an intermediary.
- The bases along the Neutral Zone are referred to as Earth outposts rather than Starfleet outposts. While it's understandable Earth would have founded them after the Earth-Romulan War and before the founding of the Federation, it's weird to still refer to them that way when Starfleet has long since assumed the defense of Earth and the Neutral Zone.
- It's stated pretty explicitly that cloaking devices, while theoretically possible, had never been before. Star Trek: Enterprise muddies those waters by giving the Romulans and the Suliban primitive cloaking tech in the 22nd century (a full century before this episode is set) and Star Trek: Discovery explicitly retcons it by giving the Klingons cloaking devices in 2256, set ten years before "Balance of Terror".
- Fantastic Racism: Lt. Stiles. From a long line of Stiles who fought in the first Romulan War. When he finds out Romulans and Vulcans look alike (and Spock himself confirms the possibility the species are related), he starts viewing Spock as a traitor. Spock saves his life during the final attack, and Stiles learns his lesson.
- Fatal Flaw: The destructive capabilities of the Romulan plasma torpedoes give everyone an Oh, Crap! moment, but it soon becomes apparent that it has very limited range.
- Give Away the Bride: Scotty does the honors.
- Heroic BSoD: Commander Hansen - his outpost is in shambles, his phaser crews dead, and the Enterprise is too far away to prevent the Romulan vessel from firing the killing blow.
- Honor Before Reason: The Romulan subcommander taunts the Commander into one final attack on a wounded Enterprise, even though the Commander knows that his Federation opponent is too dangerous to be viewed as an easy kill.
- Innocuously Important Episode: The Romulans are introduced. They go on to be major players throughout the TNG era.
- Stiles's Fantastic Racism. The Enterprise had more than its fair share of troubles with human and Human Alien antagonists. This is not seen as any reason to start viewing all humans with distrust. That Stiles himself doesn't get this emphasizes his bigotry, since while Vulcans and Romulans are obviously related, they explicitly live on different planets.
- Realising his actions could start a war, Captain Kirk sends a message to Starfleet asking for instructions. After everything is over, he gets a reply saying he's free to use his initiative. Nice to know Starfleet doesn't micromanage.
- Jerkass Has a Point: Both Sulu and Spock admit this towards jerkass statements by Stiles. First, Sulu agrees with Stiles that due to them not knowing what Romulans look like, there could be spies onboard ship, so it is reasonable to restrict peoples movements. The second instance is when Stiles advocates launching an attack on the Romulan ship, and Spock agrees - reasoning that if Romulans are Vulcanoids, they will have the same bellicosity that Vulcans once had, and therefore weakness is something we dare not show.
- It was for the wrong reasons, but Stiles' suggestion that the coded Romulan message be given to Spock wasn't unreasonable. The Romulans are clearly an offshoot of the Vulcan people, so Spock really could have some valuable insight into the Romulan language that might aid in decoding the Romulan transmission.
- Mauve Shirt: Tomlinson, so that his death at the end will be meaningful. (And no, he doesn't wear a red shirt.)
- Men Are the Expendable Gender: Modern viewers may think that, because both Angela and Tomlinson are getting married, they have an equal chance of being dead by the end of the episode. However, a 1960s audience would have found this unacceptable.
- Noble Bird of Prey: The Romulan symbol.
- Not So Different: "You and I are of a kind. In a different reality... I could have called you friend."
- Oh, Crap!:
- Everyone on the bridge (sans Spock, of course) when the Romulan ship decloaks and fires its Wave Motion Gun.
- Also when Stiles notices the leaking coolant in the phaser control room.
- The Romulan Commander also gets one. When flying through a comet, about to ambush the Enterprise, one of the crew says they're no longer being tailed. The Commander realizes that the Enterprise is ready to ambush them and he immediately orders an escape manuever.
- Old Soldier: The Romulan Commander and the Centurion, who have fought "hundreds of campaigns". Probably an exaggeration, but you get the idea.
- Outrun the Fireball: In this case, outrun a warp-speed plasma ball. While not fast enough, the plasma energy dissipates enough to weaken its deadly effects to little damage.
- If only their phasers had been operational at the time. Star Fleet Battles assures us that every 2 points of phaser damage reduces a plasma torpedo's warhead yield by 1 point.
- Phlebotinum Breakdown: The Enterprise's phaser weapons burn out after just a couple of shots. Later a plasma duct starts leaking, but at least that time the ship had the excuse of already having suffered battle damage.
- Punch-Clock Villain: The Romulan Commander turns out to be one.
- Reality Ensues: The episode opens with the wedding of a never-before-seen character, which is broken up when the Romulans attack. Throughout the episode we keep cutting back to him, until he's killed in the fight, leaving his fiancée distraught, and the whole crew mourning the death of a man whose last day alive started as the happiest of his life, indicating that, even if the audience doesn't see it, those disposable crew members are still people, and their deaths are still mourned.
- Recycled In Space:
- The 1957 WWII submarine movie The Enemy Below IN SPACE! Even the bearing of the unidentified initial contact and the captain's maneuvering orders to the helm are copied nearly verbatim. The Romulan ship is cramped and has lots of piping and conduits in all background scenes. The Enterprise's phasers act like depth charges, and at one point the Enterprise and the Romulan ship both go to Silent Running Mode, fearing to talk loudly lest the other vessel hear them.
- The Romulans, in this episode at least, were The Roman Empire IN SPACE!, as exemplified by Mark Lenard's dignified Commander character.
- Repeat to Confirm: "Phaser one...fire!" "Phaser one, fire!"
- So Much for Stealth: The Enterprise and the Romulan warbird are both attempting Stealth in Space until Mr. Spock accidentally activates a control, giving their position away.
- Space Is an Ocean: A bit more even than usual, what with all the submarine movie tropes.
- Space Romans: Mark Lenard's Romulan commander is given a hairstyle that many associate with Emperor Nero. The old warrior is called "Centurion". The subcommander is called Decius. And their ruler is called the Praetor. The old Centurion fears that Decius has friends in high places, which was also a way to climb the ladder in the Roman Empire.
- Stealth in Space: The Trope Codifier for Trek, if not all of Science Fiction. And yet, an Unbuilt Trope: it is a plot point that while under cloak the Romulan ship has the same problems with detecting the Enterprise as the Enterprise has detecting the Romulan ship.
- Sub Story: The episode is essentially a submarine duel but with starships.
- Subspace Ansible: Being so far from the nearest outpost, Kirk doesn't get a response to his intent to enter the Neutral Zone until the end of the episode.
- That's What I Would Do: How Kirk and the Romulan Commander talk about each other.Romulan: First study the enemy. Seek weakness. If I were their commander, that is what I would do.
Kirk: He did exactly what I would have done. I won't underestimate him again.
- Violence Is the Only Option: Spock of all people advocates this against the Romulans, making the case that if they've retained the barbarism of ancient Vulcans, then they must be fought.
- Wave Motion Gun: The Romulan plasma torpedo.
- Wedding Smashers: Not directly, but the Enterprise is called into battle during the wedding.
- Wham Shot: Our heroes get their first look at the mysterious Romulans...and they look just like Vulcans. Stiles in particular is shocked, and this fuels his Fantastic Racism against Spock.
- Widowed at the Wedding: Poor Angela Martine.
- Worthy Opponent
- The Romulan Commander. He's only attacking Starfleet bases because he was ordered to test a new weapon (and to test the Federation's vulnerability). He'd rather not start any more wars, and just wants to go home.
- The Commander quickly recognizes Kirk as one: "He is a sorcerer, that one. He reads the thoughts in my head."
- You Called Me "X"; It Must Be Serious: When Spock first discovers the unknown vessel is headed for the Neutral Zone, he addresses Kirk as "Jim." Later, in Kirk's quarters, McCoy addresses him as "Captain."