'Supergirl' Recap With Spoilers: "Dark Side of the Moon"

"Dark Side of the Moon" starts with Kara and Mon-El zooming across space in J'onn's ship. They get stuck in the tractor beam of a large spaceship and are "beamed" up. They're past the dark side of the moon so their comms with the DEO are on the fritz.

At the DEO, J'onn explains to Winn that Reign is gaining immunity to kryptonite.

Alex and Ruby are having snacks while watching a documentary on the cosmos. Alex explains that Supergirl is "up there" trying to find a cure for Ruby's mom, but Ruby expresses doubt. Alex and Ruby decide to go get ice cream and the two begin shopping at kiosks. Alex notices a mysterious gentleman and tells Ruby to run.

The man starts opening fire and mayhem ensues at the shopping center.

J'onn has DEO agents at Lena's lair to help her watch over Reign.

Kara and Mon-El realize they've been pulled towards a planet and as they unboard they notice an entire city on the planet. The rock that contains the cure for Sam is located near the city and they begin their search.

Alex and Ruby take to the DEO. Alex tells J'onn and Winn that somebody is out to kill her. Winn begins doing some research on who it could be and he finds out that the first person Alex ever arrested was recently released on parole. Alex convinces Winn to watch Ruby so that she can investigate the case.

Mon-El and Kara are continuing their search when Kara notices some Kryptonian ruins. As she begins reading them, her mother and a squad of Kryptonian guards confront her. Kara and her mother embrace.

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

Ruby's asking Winn's questions and a frustrated Winn starts getting upset. He goes off on a tangent until Ruby reminds him that Reign is her mother.

Alex walks into a bar and confronts Collins, the man she previously arrested. After talking with him, Alex realizes Collins' alibi is rock solid and she realizes he's not the one that's trying to kill her. Alex goes to leave on her motorcycle, but it's been rigged to explode. She narrowly escapes the explosion.

Kara and Alura are speaking with each other trying to catch up.

Mon-El's walking through the market when he sees a sick kid on oxygen. Mon-El approaches the kid's mother and asks if he can give the kid some technology that Brainy developed. After getting approval, Mon-El applies the tech to the kid and he's apparently cured of his illness.

Winn finds Ruby and talks to her about parental problems. He explains his father's villainous background. Winn asks Ruby to help out with tracking Supergirl's position.

J'onn takes Alex's shape to go on a run and try luring out Alex's would-be assassin. He's being backed up by Alex and a squad of DEO agents.

Alura introduces Kara to the High Council of Argo City. There, Kara explains to them that Worldkillers have invaded Earth and they tell her that Worldkillers are only legend on Argo City. Kara tells the Council that she needs access to the rock to help cure the Worldkillers.

J'onn is still on his run when Alex notices a sniper on a nearby roof. The sniper realizes J'onn really isn't Alex and he escapes. Alex follows in pursuit.

After hopping through the rooftops, Alex stops the sniper and realizes it's the twin brother of somebody that used to be imprisoned at Fort Rozz.

The High Council is split on whether or not to help Kara. The deciding vote is cast in Kara's favor. Kara and Mon-El take a portion of the rock back to J'onn's ship and they take off back to Earth.

Alex is sitting outside the DEO wondering about her attacker earlier in the day. She expresses displeasure to J'onn about how she didn't have the attacker on her list of suspects. J'onn sits down by her and Alex begins to wonder aloud about her life.

In Argo City, Selena — a member of the High Council — is revealed to be the cloaked woman who's been instructing Reign in her Fortress.

In her cell, Reign reveals she knows the Lena has a kill switch in place. Lena has the power to kill Reign at once, but it'd all kill Sam. Mon'El and Kara return to Lena's lair with the rock just as Reign breaks out of her cell.