It's just another day of exploration for Kirk and company. There's a planet called Argus X to be explored, a new mineral is discovered, a mysterious cloud is killing Redshirts. (The Redshirt body count for this entire episode is six, including one off screen.) The victims of the mysterious cloud of smoke are sucked dry of all blood, but with no visible cuts or punctures. Kirk remembers an incident like this from 11 years ago when he was just a Lieutenant on his first tour of duty. The guilt of the memory starts to affect Kirk. If he had just fired his phaser a little more quickly all those years ago, Captain Garrovick, half his crew and now these crew members wouldn't be dead.
Speaking of Captain Garrovick, the new ensign aboard the Enterprise is also named Garrovick...and it's no coincidence. Ensign Garrovick is the son of the late Captain Garrovick. When Ensign Garrovick is first confronted with the gaseous form, he makes the same mistake Kirk made all those years ago by hesitating to fire. Kirk, rather than sympathizing, becomes irate with the young man. Kirk develops an insatiable obsession with destroying this creature.
Can Kirk take down this blood thirsty monster without becoming a monster himself?
Tropes for this episode include:
- Air Vent Escape: How the cloud creature gets into Garrovick's quarters. Being a mist, it doesn't even have to take the grid off.
- Anti Matter: Phaser fire has no effect on the vampiric cloud. Nothing less than a matter/antimatter bomb will destroy it. It will be difficult to destroy the creature without destroying whoever sets the trap for it.
- The Bait: After the cloud vampire chugs down that jar of blood faster than they thought it would, Garrovick attempts to knock Kirk out and take his place as the bait. Kirk recovers fast enough to tell him "consider yourself on report" and carry out his original plan to beam out right before detonating the bomb.
- Call-Back: Kirk once mentioned to Bones that cordrazine is a tricky medicine to use. Nurse Chapel shows that she herself is hesitant to use it.
- Death by Transceiver: Rizzo's party has encountered the vampire cloud.Rizzo: [Activates communicator] Captain?
Kirk: Kirk here.
Rizzo: Captain, there's a strange cloud, sir. [It reaches him and he starts choking] Cloud, cloud.
Kirk: Fire into it immediately!
Rizzo: [Heard over communicator] Help me. Help! [Dies]
- Deer in the Headlights: Kirk and Garrovick both froze in fear the first time they saw the mysterious cloud. Eventually, they learn that it didn't matter anyway. Phaser fire has no effect on the cloud.
- Dodge the Bullet: We're told this is why the cloud is immune to phasers, getting out of the way impossibly quickly (although the effects don't reflect this at all). This leads both Garrovick and Kirk to kick themselves about how the hell they managed to miss a giant cloud at short range.
- Evil Smells Bad: Inverted - Both Kirk and one of the redshirts who survives says the smell the creature gives off is cloying, almost like being smothered in honey or molasses.
- Follow in My Footsteps: Ensign Garrovick joined Starfleet just like his father before him.
- Heroic BSoD: Garrovick, after being confined to quarters.
- Heroic Sacrifice: Played with. Spock shoves Garrovick out of the room when the cloud vampire pours in through the air vent. While it's true that Spock's Vulcan blood was instrumental in defeating another vampiric creature in "The Man Trap", he was taking a risk that it would work this time. Of course, he survives. Garrovick tries to knock out the captain, believing that Kirk's plan is a Heroic Sacrifice, but his attempt fails.
- The Hunter Becomes the HuntedSpock: May I suggest that we no longer belabor the question of whether or not we should have gone after the creature? The matter has now been rendered academic. The creature is now after us.
- I'm Cold... So Cold...: A half-conscious Rizzo remembers being cold when the cloud creature attacked him.
- I Need a Freaking Drink: When Spock comes to Bones and says "I need advice." Bones responds "I need a drink!"
- It Can Think: The first thing that convinces Spock that the cloud creature is actually a creature of at least semi-sentient nature is how it was capable of reacting to the Enterprise's attack in space and then turning around and attacking in retaliation.
- It's All My Fault: What Kirk thought for years and Ensign Garrovick thought for a bit for their Deer in the Headlights hesitation facing the cloud vampire. As it turns out, phaser fire is useless against it so they have nothing to regret.
- Moby Schtick: Not the first or last time that Trek would go to the well of Melville, given this trope's use in The Doomsday Machine, and of course, Star Trek II: The Wrath of Khan. However, this version of the story has the crew getting all the evidence needed to convince them that Kirk is right that the creature is a catastrophically deadly menace to the galaxy that has to be stopped immediately and do everything they can to help Kirk.
- In addition, the desire to destroy the creature is driven by survivor's guilt rather than revenge.
- More Expendable Than You: Garrovick attempts this, only for Kirk to get the better of him and explain sacrificing himself is still plan B.
- My Greatest Failure: How Kirk views his last confrontation with the cloud creature.
- Non-Standard Prescription: When Garrovick is brooding on his feeling of guilt, Nurse Chapel tells him that McCoy has issued a prescription for him that consists of the single word "Eat". However, it turns out she made this up.
- Not So Different: Lieutenant Kirk was very much like Ensign Garrovick. It's intimated that Captain Kirk is very much like Captain Garrovick was.
- O.O.C. Is Serious Business: As soon as he is confronted by the cloud vampire for the first time in 11 years, the usually genial Captain Kirk starts acting like he had an extra helping of bitch flakes
- Our Vampires Are Different: The cloud creature drinks blood, but does it without breaking skin, or cracking glass in the situation with the jar of blood. It is always in the form of a cloud of white smoke. Incidentally, many vampires of legend were able to take a gaseous form.
- Permission to Speak Freely: It is established that Starfleet Regulations give the First Officer and Medical Officer the right to confront the Captain if he is behaving in ways that they feel put the ship and her crew in unwarranted danger.
- Redshirt Army: This episode has the highest body count for them. One of the redshirts killed in the teaser is Lt. Leslie — but he gets better; he can be spotted wandering around the ship later the same episode, and by the next episode filmed ("The Immunity Syndrome") he is back on the bridge. The actor was Shatner's standin for the entirety of the series.
- Sci-Fi Writers Have No Sense of Scale: In real life, one ounce of antimatter would have the explosive yield of a little over a megaton, not nearly enough to wipe out half of a planet's atmosphere.
- Screw the Rules, I Have Connections!: Discussed early on with Ensign Garrovick. Despite being the son of Kirk's first CO, he says that he doesn't expect special treatment. Kirk, of course, gives him none.
- Tap on the Head: Averted. Ensign Garrovick tries to knock Kirk out in order to sacrifice himself, but it doesn't work.
- Tell Me About My Father: After Ensign Garrovick and Captain Kirk succeed in making the cloud vampire go 'splodey, Kirk offers to tell Garrovick about his father. Garrovick readily accepts.
- Too Spicy for Yog-Sothoth: The monster finds Spock's copper-based Vulcan blood inedible, and flees. McCoy wryly jokes that Spock "must have left a bad taste in its mouth" which Spock says is figuratively true.
- What the Hell, Hero?: Bones seems to have a talent for "What the Hell?" speeches. He gives one to Kirk when he believes that the captain's zeal for destroying the monster becomes an unhealthy obsession.
- You Are Better Than You Think You Are: While Kirk as a lieutenant on the USS Farragut was kicking himself for hesitating firing on the cloud creature in the first encounter, that ship's Executive Officer recorded in his log that Kirk had performed "with uncommon bravery". Kirk then gives a similar sentiment to Ensign Garrovick, pointing out that even if he had fired his phaser on time and on target it would have made no difference.
- You Called Me "X"; It Must Be Serious:
- When McCoy addresses Kirk as "Captain" instead of "Jim" after Kirk first returns from Argos X, it's the first sign that McCoy is starting to doubt Kirk's judgment.
- From the opposite side, Spock calls Kirk "Jim" while assuring him that what happened to the Farragut wasn't his fault.