A White Martian arrives on Earth looking for J'onn. Cat's estranged son Adam arrives in National City, carrying a letter from Cat that Kara had "finished" and mailed under her name.
Tropes in this episode:
- Always Chaotic Evil: The White Martians are presented as a whole species of bloodthirsty mass murderers—odd for an episode focused on Fantastic Racism.
- Though given that J'onn witnessed the destruction of his people at their hands it's almost understandable.
- Antagonist Title: The title refers mainly to the White Martian.
- Arson, Murder, and Jaywalking: Cat, not worried about dinner with her son: "I've sat down with Vladimir Putin, Pope Francis, and Taylor Swift..."
- Badass Boast: When the White Martian threatens that millions of his kind will come for his help, Supergirl simply answers 'Let them come'.
- J'onn delivers a nice one as well: "I am 317 years old. I can wear any face I choose. I speak languages your mouth can't even form. You know nothing about me."
- Call-Back: J'onn using his powers to impersonate Maxwell Lord in the previous episode allowed the White Martian to sense him, drawing it to Earth.
- Calling Parents by Their Name: Adam's argument with Cat ends with him calling her by name.
- Casting Gag: Adam is played by Melissa Benoist's former Glee co-star and then-husband, Blake Jenner.
- Central Theme: Facing the past.
- A Day in the Limelight: This is a very J'onn-focused episode.
- Debut Queue: The episode marks the debut of Adam Foster and Bizarro's official outing as "Supergirl".
- Does This Remind You of Anything?:
- J'onn describes the horrors that the Green Martian faced when the White Martians imprisoned them in labour camps and sent multiple corpses into the ditches. J'onn also mentioned how his wife and two daughters were sent to the Furnace and burnt to death.
- Senator Crane claims that aliens are invading the Earth to take up resources and even advocates building a giant dome to keep them out.
- Domed Hometown: Crane suggests building a giant dome to protect humans from aliens.
- Double-Meaning Title: The title refers mainly to the White Martian, but it can also refer to both Kara and J'onn.
- Evil Knockoff: Lord's Lab 52 plan comes to fruition in the final scene, revealing a Supergirl copy that has her basic powerset.
- Fantastic Racism:
- The White Martian sees Green Martians as insects and humans as worm food.
- Crane is bigoted against all aliens, seeing them as only here to take resources that aren't theirs. She gets better at the end of the episode after Supergirl saves her life.
- Fingore: The White Martian loses a finger during his attack on the DEO.
- Glowing Eyes of Doom: The White Martian's eyes glow white, compared to J'onn's red.
- Heel–Face Turn: Senator Crane has a change of heart at the end of the episode regarding aliens after Supergirl rescues her.
- Heroic BSoD: J'onn twice freezes at the sight of the White Martian, remembering what they did to his family and planet.
- If You Kill Him, You Will Be Just Like Him!: Supergirl talks J'onn out of killing the White Martian because then he'd be no better than their kind—and what's more, the White Martian would then have effectively succeeded in destroying the last of the Green Martians.
- I Never Said It Was Poison: The White Martian blows his cover as Miranda Crane by mentioning that a White Martian attacked the rally. Crane would only know it as a monster, not by its proper name.
- I Surrender, Suckers: J'onn pretends to give himself up to the White Martian to save Alex, only for Supergirl to swoop in and sucker punch the White Martian when he's distracted.
- It's All My Fault: J'onn can't stop blaming himself for not realizing that the White Martian infiltrated the DEO sooner, leading to the deaths of agents under his command.
- It's Personal: J'onn had enough of the White Martian terrorizing the city, so he decides to end it once and for all by killing the White Martian.
- Jerk with a Heart of Gold: This episode goes another length to prove that deep down Cat Grant is a good person, despite her flaws.
- Like a Daughter to Me: J'onn calls both Danvers sisters this at the end, in memory of his own two deceased daughters.
- Mythology Gag: The episode's title is a direct reference to Superman's classic description.
- A Nazi by Any Other Name: The White Martians are most definitely painted as Martian Nazis, including labour camps, body pits and furnaces.
- No Celebrities Were Harmed: Senator Crane is running a campaign of vicious anti-alien fearmongering, and proposes building a dome around National City to keep them out. How do you suppose the writers feel about Donald Trump?
- Out of Focus: Winn appears only in two scenes with a single line each.
- Politically Incorrect Villain: The White Martian, obviously. She (or he, or it) refers to Green Martians as insects, and thinks even less of humans.
- "The Reason You Suck" Speech: Adam gave Cat one for both being a Missing Mom and her persistent It's All About Me attitude.
- Ship Tease: Adam is obviously interested in Kara and openly flirts with her. Cat plays Shipper on Deck for them. They have a date by the end of the episode.
- Shout-Out: The portrayal of Green and White Martians owes far more to the races of the same names in John Carter of Mars than the DC Universe.
- Survivor's Guilt: Ever since J'onn escaped from the White Martians, there hasn't been a day that goes by when he isn't ashamed about being the last Green Martian alive.
- This Was His True Form:
- When the White Martian gets his finger shot off while in the form of Miranda Crane, the finger reverts to its normal form.
- Inverted when Supergirl defeats him, in White Martian form, and he suddenly transforms back into Crane.
- Wounded Gazelle Gambit: After the White Martian's disguise is blown, he goes back to his lair and pretends to be Miranda Crane again, kept alive by the White Martian. It isn't until J'onn finds the real one that they realize they've been played, and by then it's too late to stop the White Martian from taking Alex.
