- The ending is nothing but pure horror and heartbreak.
- The ending. While the ship and crew survive intact (for the most part), it still feels like a Downer Ending. The fact that Kirk points out that they couldn't save Mitchell somehow makes it worse. Mitchell was essentially Kirk's brother, with both men forced to turn on each other; Kirk to protect his beloved ship and crew, and Mitchell intoxicated and corrupted by godlike power that he never asked for; especially evident during his few brief moments of lucidity near the end of the episode, where both times, all the poor man can say is his best friend's name, unable to express anything more.Kirk: He didn't ask for what happened to him.
- The fight. It isn't hard to imagine John Williams' "Battle of the Heroes" in the background.
- Add to official losses, Doctor Elizabeth Dehner. Be it noted she gave her life in performance of her duty. Lieutenant Commander Gary Mitchell, same notation. I want his service record to end that way. He didn't ask for what happened to him.
- Spock's reaction to the Psi 2000 virus. The incurably stoic Vulcan breaks down in sobs. His explanation to Kirk of his regrets might also count, especially since Kirk is too pressed for time to listen.Spock: I never told my mother I loved her. An Earth woman, living on a planet where love, emotions, are in bad taste...
Spock: Jim...when I feel friendship for you, I'm ashamed.
- A blink-or-you'll miss it one from when Clone!Kirk goes up to the Enterprise — Kirk's intentional Out-of-Character Alert works perfectly; it takes about a minute of calm interaction before he snaps "Mind your own business, Mr. Spock. I'm sick of your half-breed interference." Spock's voice goes utterly cold as he retreats into full Vulcan mode. We find out later that this is what he does to avoid embarrassing himself when he's heartbroken. Even though he knows (or at least quickly figures out) that this cannot be his captain functioning normally, it's exceedingly painful to him to hear that.
- Spock has just told Pike that he's going to violate orders and potentially sink his career to get Pike to Talos IV in order to restore him to at least an illusion of health. Pike indicates "no" with his chair over and over, and over and over and over. One can imagine Pike throwing himself against the walls of his mind, screaming that word and wanting to protect his friend/fellow officer from such consequences.
- The ending: Lenore reveals that she killed all of the other witnesses, which horrifies Karidian, because he wanted her to remain free of that part of his past. Then when she tries to kill Kirk, Karidian takes the shot meant for him, and Lenore has a meltdown, weeping over her father's corpse.
- The final words of the Romulan Commander with Kirk over the viewscreen after an epic battle with the Enterprise and while his ship is coming apart behind him.Romulan Commander: You and I are of a kind. In a different reality, I could have called you friend.
- The final scene is pretty brutal. Kirk goes to the chapel to find Lieutenant Martine, the young woman who was supposed to get married earlier that day... and whose fiance was killed in the battle. Kirk does his best to comfort her, knowing he can't do much. Then Martine gets her own Tear Jerker... combined with a Heartwarming Moment and quiet Moment of Awesome. She looks Kirk in the eye and calmly says, "I'll be all right." And she means it. As agonizing as losing her fiance is, she can take it.
- The "death" of Landru is surprisingly sad in its own way. While Kirk is right in destroying it, hearing Landru cry out for its creator to save it as it explodes makes one wonder if perhaps the alien computer was sentient after all.
- Spock says about Omicron Ceti III that, for the first time in his life, he was happy. Awww, Spock!
- The Bittersweet Ending. What makes it even more effective is that as Spock says the words below, the camera pans to Kirk, who is completely breaking down in tears. He does not come anywhere close to tears again until Spock's death in Star Trek II: The Wrath of Khan.McCoy: I could have saved her! Do you know what you just did?Spock: He knows, Doctor... he knows.
- Kirk's solemn last words of the episode just put the cap on it. He sounds gutted:Kirk: ...Let's get the hell out of here.
- Let's not forget that, for its day, Kirk using the word "hell" on screen was a Precision F-Strike, an emphasis of just how much he is hurting.
- The original screenplay by Harlan Ellison was even more of a tearjerker, especially thanks to the inclusion of a legless World War I veteran called Trooper who is murdered as a result of the Enterprise crewmembers' presence in the past. Unlike Edith Keeler's survival, Trooper's death doesn't affect the time stream, and Kirk's reaction to the idea that the poor guy's life didn't matter is wrenching.
- After Spock thinks he's killed Kirk:T'Pau: Live long and prosper, Spock.
Spock: I shall do neither. I have killed my captain...and my friend.
- Spock's horrified expression when he comes out of the blood fever and realizes what happened. You can easily imagine what the poor guy is thinking as he shuts down. Dealing with Kirk's death under normal circumstances (say, if a mission went wrong) would be heartbreaking enough, but Spock wakes up to find himself standing over his best friend's lifeless body, the weapon that killed him still in his hands.
- Spock's background potentially makes everything even more heartbreaking. The guy has already gone through an amount of discrimination and bullyingnote that has driven some people to villainy or to suicide, and his only response is to close himself off and work harder for acceptance. But when he realizes he's killed one of the only people to accept him (even if it's not really his fault), he breaks instantly, shutting down and wanting to die.
- Leonard Nimoy loved this episode and threw himself into it, doing some of his greatest acting ever. He later said that in the "I shall do neither" scene, he was holding back tears and could barely speak the lines. Although he denies he or Shatner did anything deliberate to suggest the Ho Yay some fangirls insist is canon, he says that the "I shall do neither" line best defines Spock's attitude towards Kirk.
- While he certainly isn't very likeable, Apollo's death at the end is surprisingly sad, with his final moments making him out to be less a ruthless tyrant than a Jerkass Woobie who just wanted to be loved. In the end, it's easy to empathize with Kirk and McCoy when they lament being forced to fight him.McCoy: I wish we hadn't had to do this.
Kirk: So do I. [The Greeks] gave us so much. The Greek civilization, much of our culture and philosophy, came from the worship of those beings. In a way, they began the Golden Age. Would it have hurt us, I wonder, just to have gathered a few laurel leaves?
- It's a small moment, but when Kirk finally catches the strange figure following the crew around the Everything Trying to Kill You forest, he grabs him and punches that sorry bastard right in the face. And the poor guy is horrified and starts crying because, as it turns out, violence just isn't a thing on this planet. An apologetic Kirk immediately has to reassure him that they come in peace.
- Even worse, this is the episode where Kirk loses three Red Shirts in rapid succession, one of whom Kirk knew very well. Spock tries to reassure Kirk, but he's just heartbroken.
- Under Vaal's instruction, the people gather in a circle and are taught how to kill the crew. Needless to say, it's pretty horrifying to watch the most innocent of people become corrupted just like that.Spock: The good doctor was concerned that the Vaalians achieve true human stature. I submit there's no cause for worry. They've taken their first step. They've learned to kill.
- Decker's anguished description of how he lost his entire crew.Kirk: Matt, where's your crew?
Decker: On the third planet...
Kirk: There is no third planet!
Decker: [looks up at Kirk in horror and shame] Don't you think I know that? There was, but not anymore! They called me, they begged me for help—four hundred of them! I couldn't... I—I couldn't...
- Kirk begging Decker to come back and let them find another way besides a Heroic Sacrifice to destroy the creature. He doesn't listen.Kirk: Matt, we're stronger with you than without you!
- The argument between Amanda and Spock. recounting his painful childhood, her storming out in tears, his raised hand at the door, unable to do anything more...Amanda: Spock, you must turn command over to somebody else.Spock: Mother, when I was commissioned, I took an oath to carry out responsibilities which were clearly and exactly specified.Amanda: Any competent officer can command this ship; only you can give your father the blood transfusions that he needs to live.Spock: Any competent officer can command this ship under normal circumstances. The circumstances are not normal. We're carrying over one hundred valuable Federation passengers. We're being pursued by an alien ship. We're subject to possible attack. There has been murder and attempted murder on board. I cannot dismiss my duties.Amanda: "Duty?" Your duty is to your father.Spock: I know, but this must take precedence. If I could give the transfusion without loss of time or efficiency, I would. Sarek understands my reason.Amanda: Well, I don't. It's not human. That's not a dirty word. You're human, too. Let that part of you come through. Your father's dying.Spock: Mother, how can you have lived on Vulcan so long, married a Vulcan, raised a son on Vulcan, without understanding what it means to be a Vulcan?Amanda: If this is what it means, I don't want to know!Spock: It means to adopt a philosophy, a way of life, which is logical and beneficial. We cannot disregard that philosophy merely for personal gain, no matter how important that gain might be.Amanda: Nothing is as important as your father's life.Spock: Can you imagine what my father would say if I were to agree, if I were to give up command of this vessel, jeopardise hundreds of lives, risk interplanetary war, all for the life of one person?Amanda: When you were five years old and came home...stiff-lipped, anguished...because the other boys tormented you, saying that you weren't really Vulcan. I watched you, knowing that, inside, that the human part of you was crying. And I cried, too. There must be some part of me in you, some part that I still can reach. If being Vulcan is more important to you, then you'll stand there speaking rules and regulations from Starfleet and Vulcan philosophy, and let your father die. And I'll hate you for the rest of my life.Spock: Mother—Amanda: Oh, go to him. Now. Please.Spock: I cannot.[Amanda slaps him across the face and storms out]
- Kirk's descent into senility and paranoia is made more painful by the reactions of those around him—especially Spock, who looks sadder and sadder as the episode progresses. When, after the competency hearing, Kirk calls him a traitor and adds he never wants to see him again, Spock leaves looking, by Vulcan standards, like he's about to cry.
- Travis Mayweather's whole family died in mysterious circumstances, and the last thing they are known to have done is accidentally screw up a culture.
- After Spock is chosen over Bones for the dangerous mission, Bones walks him down to the hanger deck and Spock tells him, with just a touch of sarcasm, "Wish me luck." Bones refuses to say it until Spock is out of earshot. Later, when Spock's mission seems to have turned into a suicide run, Spock calls over the comm, "Tell Dr. McCoy he should have wished me luck." The look on Bones's face...
- When M5 goes haywire and begins attacking several Federation starships that are unprepared as they think this part of a war game exercise, a clearly-agonized Kirk pounds his chair and can only watch helplessly as the computer that has hijacked control of his ship proceeds to destroy one Federation ship and severely damage three others, causing the deaths of hundreds of officers and crew.
- Daystroms plight is tragic as well. A prodigy at a young age, his early successes became a noose around his neck, because, as McCoy points out, where do you go from up? The whole reason he built the M5 was to preserve lives, yet, in his desperation to create something that could even begin to match his prior breakthrough, his creation proceeds to kill the entire crew of a starship.
- Poor Flavius getting shot while trying to save Spock and McCoy from public execution.
- The ending. Kirk loses his unborn child and his wife within minutes of one another.
- Maybe it isn't the greatest episode, but it does have a couple of tragic moments, most notably the happy smiles from the children looking at footage of their parents, which turn to horror and tears when they discover their parents are all dead.
- The Downer Ending. Lokai and Bele lose their home planet and entire species, and even then they still hate each other...because that hatred is all they have left.Sulu: But the cause they fought about no longer exists. Does it matter now which one was right?Spock: All that matters to them is their hate.Uhura Do you suppose that's all they ever had, sir?Kirk: No, but that's all they have left. [dejected] Warp factor 4, Mr. Sulu. Starbase...4.
- The Bittersweet Ending: Kirk loses a woman he fell hard for, even though she was an android, and ends the episode facedown at his desk in sadness. Which leads to this conversation between McCoy and Spock, which ends in a very poignant moment:McCoy: You see, I feel sorrier for you than I do for him, because you'll never know the things that love can drive a man to: The ecstasies, the miseries, the broken rules, the desperate chances, the glorious failures...and the glorious victories. All of these things you'll never know, simply because the word "love" isn't written into your book. Good night, Spock.[McCoy leaves, and Spock quietly walks over to a sleeping Kirk and gently applies a mind-meld]Spock: [beat] ...Forget.
- Kirk is able to get Spock and McCoy back to the present, but Zarabeth, the woman who helped them and whom Spock has come to love, has to remain behind, condemned to live out the rest of her life alone in Sarpeidon's ice age.Spock: It happened, but that was five thousand years ago and she is dead now. Dead and buried long ago.
- The deaths of so many Red Shirts. Yes, the death of Red Shirts was a Running Gag, but let's be honest: Some of these deaths were very heartbreaking.
- Poor Yeoman Thompson, the only female red shirt to die onscreen in TOS, who was turned into a mineral cube by Rojan and crushed in "By Any Other Name."
- The young engineer Harper who got vaporized by a plasma flow activated by M-5 to restore its power supply. The worst part is how Daystrom tried to rationalize it as Harper simply "getting in the way."
- While it's not mentioned afterward (figures), the two security officers who got beamed into open space while Sulu and Chekov were under the induced illusion that the ship was still in orbit of a planet in "And the Children Shall Lead." Poor guys...
- The death of the man who was about to be married in "Balance of Terror" and his fiancée's reaction at the end of the episode, is probably the saddest one in the series.
- Part of this is that, Running Gag it may have become, to Kirk, the fact that these crewmen died on his watch is clearly a personal failing—he may have saved the ship, but his role as captain is to protect those men and women under his command, so to him, not coming home with everyone means he still failed. Combine that with the number of crewmen killed during the series, and the poor captain seriously comes off as a Stoic Woobie.