Kara and Mon-El's hunt for the Harun-El stone leads them to the Kryptonian city of Argo, and Kara's mother Alura.
Tropes:
- Actor Allusion: Once again, Tim Russ plays a Human Alien arguing for the logical course of action instead of the emotional one.
- The Alcoholic: Sheriff Collins has become one after his prison release.
- Artistic License – Space: Argo City is said to be five light years from Earth, yet later dialogue refers to it as if it's still within the solar system.
- The Atoner:
- Alura regrets the choices she made as Krypton's judge, considering them her greatest mistake. One of the first things she asked Kara was whether the prisoners she had condemned to Fort Rozz survived.
- Also ex-Sheriff Collins, who regrets the boy's death and doesn't blame Alex for helping to put him in prison, claiming he deserved the punishment.
- Bond Villain Stupidity: Alex would-be killer takes time to explain his reasoning to Alex instead of shooting her or pushing her off the edge right away.
- The Bus Came Back:
- Sheriff Collins from Midvale is now free on parole and living in National City.
- Alura. She survived along with the city of Argo.
- Bus Crash: Zor-El died in his efforts to make life in Argo sustainable.
- Canon Character All Along: The mysterious priestess responsible for transforming Sam into Reign is revealed to be named Selena, a nod to the Big Bad of the 1984 Supergirl film who had been made a Canon Immigrant during Supergirl (Rebirth). And she's still a witch in the show's version, albeit Kryptonian instead of human.
- Cliffhanger: The episode ends with Reign breaking free and her and Kara facing off.
- Continuity Nod:
- Alex mentions how she was crucial in having Sheriff Collins arrested when she was 17.
- The Hellgramite, Griggs, Hannibal and Rick Malverne are mentioned as potential candidates who'd want to hurt Alex.
- Kara talks to Alura about the Fort Rozz escapees and how Astra and Non tried to wreak havoc on Earth.
- Decided by One Vote: Selena is the deciding vote on whether or not Supergirl gets the rock she came for, though it's implied she knows it won't work out as planned when she votes in Supergirl's favor.
- Domed Hometown: Argo survived Krypton's destruction thanks to an energy shield developed by Zor-El.
- Drives Like Crazy: Alex, apparently, as it gave Ruby motion sickness.
- External Combustion: Alex's motorcycle is rigged to explode, though it helpfully beeps and takes nearly ten seconds to actually go off once she tries to start the engine.
- Fantastic Racism: Subverted. Alura recognizes Mon-El as the Prince of Daxam, and it briefly seems like she's prejudiced, but she's not. Since both planets are gone, such racism is pointless.
- Godzilla Threshold: Lena has set up a lethal dose of Kryptonite for Reign in the event that containing her is no longer possible. When she reluctantly triggers it, it does nothing.
- Jerkass Ball: Winn briefly grabs it when he has to watch Ruby. He quickly apologizes and the two start bonding over their parent issues.
- The Nose Knows: The alien trying to kill Alex isn't fooled by J'onn's shapeshifting because he can distinguish Alex's scent from J'onn's, even though he's several buildings away from both.
- No-Sell: Reign has completely adapted to the Kryptonite and the sense-blocking properties of Lena's forcefield, ignoring a lethal dose of the former and speaking right through the latter as if it weren't there.
- Not Me This Time: Collins wasn't the one trying to kill Alex — it was the brother of some random alien Alex put into Fort Rozz.
- Red Herring: At first it seems like Collins is in National City to kill Alex, given his seemingly unlikely decision to move within six blocks of her apartment, but he's not.
- Reformed Criminal: Sherrif Collins feels terrible about his past deeds.
- The Reveal:
- Kara's mother, and a number of other Kryptonians, are alive and living on Argo City.
- The priestess behind the Worldkillers, who has been unnamed up until now, is named Selena, and is a member of the Kryptonian council on Argo City.
- Sadistic Choice: In case Kara and Mon-El don't return in time, Lena is left with the choice of giving Reign a lethal dose of Kryptonite or letting her break free.
- So Proud of You: Mon-El admires Supergirl as an inspiration for him and people from the future.
- Strike Me Down with All of Your Hatred!: Reign tries to goad Lena into using the Kryptonite kill switch, well aware that it will fail when she does.
- Superman Stays Out of Gotham: The trope has been an ongoing issue throughout the Reign arc, but is particularly noticeable here. After a brief namedrop with Alura, not only is Kal-El never mentioned again, it is stated outright that only Supergirl can save Earth from Reign, with no mention given of enlisting Superman even as back-up.
- Terminally Dependent Society: Argo City owes its survival to a car-sized chunk of Harun-El that powers the shield and purifies the atmosphere. This is why they are so reluctant to part with even the smallest bit of it, despite the threat Reign poses to Earth.
- There Is Another: An entire city of Kryptonians — Argo.
- Villain with Good Publicity: Councilwoman Selena, who was the deciding vote to give the Harun-El to Kara, is secretly the Priestess of the Worldkillers and the one who triggered their transformation.
- We Will Have Perfect Health in the Future: Mon-El cures a child with lung problems using a device built by Brainiac 5 that can cure any normal disease simply by wearing it for a week.
- Wham Episode: Kara finds an entire city of Kryptonian survivors, including her mother.
- Wham Shot:
- For those familiar with the comic books, the shot that reveals the existence of Argo City on the surface of a fragment of Krypton.
- As Supergirl stands before the Argo Council, the first member we see is the woman whose hologram was leading the Worldkillers on Earth.
