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"On Argo, we learn from Krypton's mistakes. We look to our past for edification. My mistakes were the biggest of all."
Alura Zor-El

"Dark Side of the Moon" is the twentieth episode of the third season of Supergirl, and the sixty-second episode overall. It aired on May 28, 2018.




Guest starring[]



"Dark Side of the Moon" begins with Kara and Mon-El zooming across space in J'onn's ship. They stall out in the tractor light emission huge spaceship and are "transmitted" up. They're past the clouded side of the moon so their comms with the DEO are acting up.

At the DEO, J'onn discloses to Winn that Reign is picking up resistance to kryptonite.

Alex and Ruby are having snacks while viewing a narrative on the universe. Alex clarifies that Supergirl is "up there" attempting to discover a remedy for Ruby's mother, however Ruby communicates question. Alex and Ruby choose to go get frozen yogurt and the two start shopping at stands. Alex sees a dangerous-looking man and advises Ruby to run.

The man lights starting to shoot and disorder results at the strip mall.

J'onn has DEO operators at Lena's refuge to assist her with looking out for Reign.

Kara and Mon-El acknowledge they've been pulled towards a planet and as they unboard they notice a whole city on the planet. The stone that contains the solution for Sam is situated close to the city and they start their inquiry.

Alex and Ruby take to the DEO. Alex tells J'onn and Winn that someone is out to execute her. Winn starts doing some exploration on who it could be and he discovers that the first individual Alex ever captured was as of late discharged on parole. Alex persuades Winn to watch Ruby with the goal that she can explore the case.

Mon-El and Kara are proceeding with their inquiry when Kara sees some Kryptonian ruins. As she starts understanding them, her mom and a crew of Kryptonian watches face her. Kara and her mom grasp.

Alura clarifies that Argo, the city they're in, is comprised of survivors from Krypton. Alura takes the pair to the Black Rock of Utica.

Ruby's posing Winn's inquiries and a disappointed Winn begins getting furious. He goes thinking about something irrelevant until Ruby advises him that Reign is her mom.

Alex strolls into a bar and faces Collins, the man she recently captured. In the wake of conversing with him, Alex understands Collins' alibi is unshakable and she understands he's not the one that is attempting to murder her. Alex goes to leave on her cruiser, however it's been fixed to detonate. She barely gets away from the blast.

Kara and Alura are talking with one another attempting to get up to speed.

Mon-El's strolling through the market when he sees a sick child on oxygen. Mon-El moves toward the child's mom and inquires as to whether he can give the child some invention that Brainy created. In the wake of getting endorsement, Mon-El applies the tech to the child and he is cured.

Winn discovers Ruby and converses with her about parental issues. He talks about how evil his dad was. Winn requests that Ruby help with tracking Supergirl's position.

J'onn takes Alex's shape to go on a run and take a stab at attracting out Alex's future professional killer. He's being sponsored up by Alex and a crew of DEO specialists.

Alura acquaints Kara with the High Council of Argo City. There, Kara discloses to them that Worldkillers have attacked Earth and they reveal to her that Worldkillers are just legend on Argo City. Kara tells the Council that she needs access to the stone to help fix the Worldkillers.

J'onn is still on his run when Alex sees an expert rifleman on a close by rooftop. The expert marksman knows that J'onn truly isn't Alex and he get away. Alex follows in interest.

In the wake of jumping through the housetops, Alex stops the expert rifleman and understands it's the twin sibling of someone that used to be detained at Fort Rozz, later identified as an alien from Naja Falk 7 who tried to kill Alex.

The High Council is part on whether to help Kara. The concluding vote is thrown in support of Kara. Kara and Mon-El return a part of the stone to J'onn's ship and they take off back to Earth.

Alex is sitting outside the DEO pondering about her aggressor prior in the day. She communicates disappointment to J'onn about how she didn't have the assailant on her rundown of suspects. J'onn plunks somewhere near her and Alex starts to ponder out loud about her life.

In Argo City, Selena — an individual from the High Council — is uncovered to be the shrouded lady who's been training Reign in her Fortress.

In her cell, Reign uncovers she realizes the Lena has an off button set up. Lena has the ability to kill Reign immediately, yet Sam would die too. Mon-El and Kara come back to Lena's den with the stone at the same time that Reign breaks out of her cell.




  • Argo City is Supergirl's home city in the comics. It also appeared in 1984's Supergirl, and is from where Kara arrived on Earth in search of the Omegahedron.
  • Winn mentioned that he has 6 satellites monitoring Supergirl and Mon-El and had his radio dialed up to 11. Winn later says, "Better crank that baby up to 12". This is a quote from This Is Spinal Tap, a 1984 American rock mockumentary.
  • The little boy whom Mon-El heals in Argo City is named Val. Though not directly related to Supergirl, Kara's great-great grandfather, Val-El, appears in the series Krypton.
  • When talking about people she arrested/helped arrest in her past, Alex mentions Ronald Collins and Rick Malverne.
    • Interestingly, Alex never considers Samuel Bernard as a potential suspect, despite the fact that she got him arrested after outing his illegal love affair with Josie to the authorities and Samuel would've been out of prison by 2018 if still alive.
  • When Kara is pleading to the High Council of Argo, behind her are two sets of two rings, which are identical to the spinning rings that held Zod, Ursa, and Non during the trial scene in the movie Superman. The two scenes are thematically similar.
    • Notably, Selena being given the vote to break the tie to give away a piece of the Harun-El to Kara is similar to when Jor-El is given the responsibility to break the tie to put Zod in the Phantom Zone in the movie.
  • In several adaptations, the dark side of the moon is where the wizard Shazam exiled Black Adam.


  • The Harun-El is said to be five light-years away, and while the confines of science-fiction allow for Kara and Mon-El to travel that far with J'onn's FTL drive, it would still be impossible for Winn to pick up any sort of signal from them using conventional Earth satellites, as light-speed is the speed limit of all information in the universe. Thus, even if Winn picked up a signal from the rock that was traveling at the speed of light, it would still take five years to arrive.
  • Considering that Kara says in Not Kansas that she grew up in Argo City, and that it was rebuilt to be identical, it is strange that she did not recognize it until she reached the monument, or the language that its inhabitants were speaking.