Kara is cooking turkey with laser vision. Winn and James are fighting over who gets to tell Kara about Guardian. Alex tells them that she has bigger news to share so they aren’t ruining it.
During dinner they are going around the table to say what they are thankful for and when it’s Alex’s turn she starts to ramble to get the nerve to come out but she is interrupts when a wormhole opens over the table.
At the DEO, Kara, Winn and Alex discuss what it could mean and they think it has something to do with cadmus. Kara says that is gonna be sneaky and talk to Lena about her mother. Winn hacks Lena’s phone.
Kara interviews her. She starts out friendly but the questions get more pointed and Lena tells her she needs to go to a meeting. After Kara leaves, Lena calls her mom for a meeting.
Mon-El is at the alien bar. Cyborg Superman is there as well setting up a weapon, and then hurrying out. Mon-El follows him and they fight in the alley while the weapon releases a gas inside. It kills all the aliens. but no humans.
Mon-El is in quarantine because of what he had been exposed to. He explains what happened at the bar and Alex says that she wants to bring her mother in to consult. Kara and J’onn will remain in quarantine until they know what’s up.
Lena is talking to her mother about Lex and the Luthor name. She says that there’s a reporter sniffing around and she’s smart. Lillian denies it and Lena cries.
Kara and Mon-El are playing monopoly and talking about his potential crush on her. He says its not the case. Then he starts coughing. He’s infected to and according to Eliza, the weapon is kryptonian. Kara realizes it is from her blood, that they broke into the Fortress of Solitude. She goes there to investigate and is attacked as an intruder.
She finds out that Cadmus was there to acquire Medusa. It was created by her father to protect Krypton from other aliens. It will kill all other aliens. She reports back to the DEO about her findings and nexplains her father’s involvement.
Alex and her mother are working on the cure but her mother knows she has a secret and asks her if it has anything to do with Maggie, since she apparently talks about her a lot.
Kara is on a balcony overlooking the city from DEO headquarters. Hank joins her and she tells him about the things that her parents did. He defends there actions before having an episode. He tells Kara not to tell Alex because they need to focus on medusa.
Eliza and Alex come and tell them that there is only one rare isotope that can be used for the cure. It happens to be at L-Corp and if cadmus gets control of it the whole city is in trouble. Supergirl takes off. Alex calls Maggie for backup.
Cyborg Superman heads into the L-Corp building. He sets off the metal detector and the guard tells him to stop. He attacks the guard and Supergirl shows up in the nick of time to save the guard and throw down with Cyborg.
Lena turns up and Supergirl protects her. They continue to fight and NCPD comes in to try and help fight the Cyborg. Maggie gets injured in the process.
Winn, Hank and Kara talk about trusting Luthors. She thinks that Lena is above board but no one else feels that way so she decides to take matters into her own hands.
Supergirl confronts Lena about her mother’s cadmus project. She wants help finding her but Lena won’t have it. She believes her mother is not the “devil incarnate” and won’t help Supergirl.
Alex stitches up Maggie and tells her that she came out to her mom. She thanks Maggie for helping her accept her new normal.
Kara is sitting with Mon-El when he wakes up. She tells him about her birth father being responsible for his pain. He kisses her.
Lena summons her mother again. They talk about the isotope and cadmus. Mrs. Luthor didn’t think Lena believed in the cause but Lena says that maybe she just didn’t know her own daughter.
Winn’s alarm goes off. Cadmus has the isotope on the move. A video is released. Hank and Kara are the only options. They have to go and save the day. Lena is the at the port with her mother about to release the virus. She has to do it to prove her loyalty. Supergirl and Hank show up to stop them but Lena launches the rocket.
Supergirl gives chase while Hank fights the Cyborg. The Luthors make a hasty exit. Kara can’t stop the rocket so she returns to fight the Cyborg. He is no superman. Lena switched out the isotope. The virus released doesn’t kill the aliens. She also called the police.
In space there is a meeting. A few people are trying to track down Mon-El. Eliza has cured both him and Hank in the process.
Kara and Mon-El talk about what happened when he was sick. He doesn’t remember.
Alex is sitting by herself when there’s a knock on her door. Maggie is there with pizza and beer. Alex asks if there’s a new case but there’s not. Maggie was faced with her own mortality and realized she should do what she wants, kiss who she wants, and that’s Alex. So they kiss.
Barry aka The Flash and Cisco turn up to ask Kara to help them with something. She agrees to go.
A lot of important stuff happens. Lena turns her back on being a Luthor to help aliens. Mon-El and Hank are healed. Kara finds some stuff out about her family. But come on. Alex and Maggie getting together is the most important development. How long until they break them up though? Oh, and the laser baked turkey was awesome too. I thought this was a good episode and I don’t watch the other shows (yet. That’s on the schedule for the six week hiatus) so I was glad this wasn’t too crossover heavy.
Supergirl returns Jan. 16 at 8 p.m.