M'gann fears that a White Martian named Armek has come to drag her back to Mars, and while J'onn and Kara strive to protect her, they also face the frightening possibility that anyone in the DEO could be him in disguise.
Tropes in this episode:
- Absentee Actor: Mehcad Brooks, James Olsen, does not appear in this episode.
- Always Chaotic Evil: Subverted with the White Martians, and not only M'gann herself—she leaves Earth in the end to try to find and rally more open-minded individuals of her people against their racist society.
- Alone with the Psycho: After the group finds out that Armek was impersonating Winn, everyone in the building split off into teams to search the building to find the real Winn. J'onn and M'gann pair up to search one area while Agents Vasquez and Demos search the north wing, leaving Kara and Alex to search the basement. Unfortunately for Kara, it turns out that "Alex" is another White Martian in disguise.J'onn: [over the comms to Kara] We were wrong! There are two White Martians in the building.
J'onn: It's Alex! The other White Martian has shape-shifted into Alex!
Kara: [turns around nervously to face "Alex"] ... Alex?
White Martian!Alex: [grinning sinisterly] You guys are so dumb. [growls and knocks Kara to the ground]
- Anguished Declaration of Love: J'onn gives one to M'gann before the battle with Armek, and M'gann returns it to him before she leaves for Mars.
- Armor-Piercing Response: When Kara once again tries to talk Winn out of the Guardian thing, he shuts her down quickly, saying that it is not just James's, but also his calling.
- Arranged Marriage: M'gann and Armek were bonded for life as mates when they were young, as is White Martian custom.
- Big Damn Heroes: After seemingly defeated, the second White Martian rises up again and prepares to strike at J'onn, but Alex enters the scene and shoots him down with the gun she got from Slaver's Moon.Alex: Have I mentioned how much I love my new gun?
- Blatant Lies: Despite her saying that it's okay, one can clearly see how upset Kara is about the fact that her sister wants to go to a concert with her girlfriend instead of coming to her Earth birthday (the anniversary of the day she landed).
- Chekhov's Gun: A literal one. Alex uses the gun she called dibs on at Slaver's Moon to shoot the second White Martian right when he's about to strike J'onn.
- A Day in the Limelight: For both J'onn and M'gann.
- Double-Meaning Title: It's an episode with both a Multi-Character Title and Literary Allusion Title.
- When everyone is placing their hands by the Bunsen burner flame to check who the White Martian is, Alex stares at the flame warily and stays far away from it, giving us a hint that she is a White Martian in disguise.
- When J'onn and M'gann are speaking in Martian, the camera zooms in on Alex's face.
- Later, when Alex and Kara are searching the basement for Armek, Alex signals to Kara using some hand signals to look around the corner. Kara has no idea what those hand signals mean. But Alex would know her sister well enough to know that Kara doesn't know these hand signals; in fact, Alex has never used hand signals with Kara before, hinting that "Alex" here is actually a White Martian.
- From Bad to Worse: So if being trapped in the DEO with a shape-shifting killer alien isn't bad enough, how about said alien using Winn's access to mess with the building's reactor, setting it to explode, and take out a large chunk of National City along with it?
- Glamour Failure: Close proximity to an open flame causes a Martian (both Green and White) to revert to their natural body.
- Green-Eyed Monster:
- Kara has this reaction towards Maggie, given that Alex cancels plans for her Earth Birthday to go to a concert with her.
- Kara shows a slight envy towards Eve, after she finally realizes her feelings for Mon-El.
- Impostor Exposing Test: J'onn uses the flames of a Bunsen burner to see who morphs back into a White Martian.
- Irony: Alex, who complained her sister was neglecting her back when Kara was hanging out with Superman, now completely forgets about Kara's birthday because she's busy having fun with her girlfriend.
- It's All My Fault: M'gann is quick to blame herself for the danger that J'onn, Kara, and everyone at the DEO find themselves in, since the White Martians are after her.
- Know When to Fold 'Em: When Supergirl arrives on the scene, Armek (who was fighting M'gann and J'onn) flies away instead of fighting three opponents at once.
- Literary Allusion Title: To Ray Bradbury's The Martian Chronicles.
- Locked in a Freezer: J'onn seals the DEO and everyone inside off from the outside world to prevent Armek from escaping.
- Marital Rape License: Not directly stated, but more than subtlety implied by M'gann in regards to her Arranged Marriage with Armek. When he approaches her in the bar, he leers that "the nest has been cold" since she left, to which she retorts that it always was.
- Moral Myopia: From the White Martians' point of view, the Green Martians are monsters, and disguising yourself as one of them or helping them is akin to a war crime.
- Multi-Character Title: J'onn, M'gann, and the two White Martians are all covered by the title.
- A Nazi by Any Other Name: Armek proudly boasts about how much of a paradise Mars is, now that the green "vermin" have been wiped out, and is seemingly looking forward to doing the same to humanity. M'gann isn't exaggerating when she describes him as the worst of the worst of her people.
- Not Helping Your Case: When Kara tries to explain to Mon-El why she isn't interested in him, she unintentionally keeps insulting him with everything she says.
- Out of Focus: The last episode ended with a wedge being formed between Kara and the men in her life. Besides brief scenes between Kara and Mon-El, and her and Winn, this episode focuses more on J'onn and M'gann, and Kara's relationship with Alex.
- Put on a Bus: M'gann decides to return to Mars to help organize peaceful revolution with other White Martians who think like her.
- Psychic Link: The two White Martians are able to use this to impersonate Winn and Alex accurately.
- The whole setup of a shapeshifting alien in a locked down base is straight from The Thing (1982).
- The episode's title refers to Ray Bradbury's classic novel/short story collection.
- Maggie surprises Alex with Barenaked Ladies tickets, and "One Week" plays over the scene of them getting ready for the concert, before Alex leaves to talk to Kara and gets tangled up in the events at the DEO. Later, Winn says that it feels like they were locked down in there for "one week," prompting Alex to call Maggie and apologize.
- A seemingly beaten alien suddenly stands up behind the heroes, roaring, only to be taken out by a girl with an alien gun. Yeah, we've seen that.
- Shapeshifter Guilt Trip: The White Martian disguised as Alex stays in that form to fight Kara. When it lands its first blow on Kara, Kara hesitates, stunned for long enough that the White Martian teases her for being too afraid to fight.
- Spot the Imposter: J'onn uses fire from a Bunsen burner to expose the infiltrating White Martian among the DEO agents.
- Tempting Fate: A mere moment after M'gann tells J'onn that her people aren't here yet, Armek arrives.
- Trash Talk: The White Martian disguised as Alex really gets a kick out of insulting Kara while it fights her.White Martian!Alex: What's wrong, Supergirl? Too afraid to put up a fight?
White Martian!Alex: To tell you the truth, I'm glad they found your sister. It's so exhausting pretending to care about your silly little feelings.
Kara: If you hurt her—
White Martian!Alex: You'll what? Whine at me?
- Unrequited Love Switcheroo: Just as Kara realizes her feelings for Mon-El, he's moved on to Eve.
- Wham Line: "We were wrong! There are two White Martians in the building. Its Alex! The other White Martian has shape-shifted into Alex!"
- Wham Shot: M'gann and J'onn find Winn cocooned to the ceiling. Then they see another on a nearby wall and realize that a second White Martian is impersonating Alex.
- Why Did It Have to Be Snakes?: Like his comic incarnation, J'onn is afraid of fire.
- A Wolf in Sheep's Clothing: Armek can disguise himself as anybody.
- You Are a Credit to Your Race: J'onn has fully gotten over his hatred against M'gann.