Superman is wailing on Supergirl. Rhea is using silver kryptonite to control him. He doesn’t see Kara. He sees his worst enemy, Zod. They fly out of the ship and start fighting on the streets of National City.
The DEO gets the signal and checks it. Alex sees that it is Kara so she and Maggie head downtown and see the fight firsthand. After a long battle, Kara knocks Clark out and there is a lot of destruction.
Kara and that dude wake up on bed together and talk about her mother. It’s not real though. She’s actually at the Fortress recuperating with Clark. Alex is watching over them.
Lena is drinking alone in her office when Lillian shows up. They talk about her upbringing and then moves on to science. She might be able to save the world with some her brother’s tech.
Clark really believed he was fighting Zod. He can’t believe it. Alex asks about weaponry and he says there is none but there may be information. He looks in the archives and then they head to the DEO. Winn fumbles over Superman and plywood is there.
They present the information they got at the Fortress but plywood is all no. Then an alert goes off. Kara wants a face to face with Rhea so they video chat and she basically challenges her to a winner take all duel.
Dude is all Kara no don’t do it and she’s all I have to. He thinks she should let Superman do it because obviously men are better fighters but Superman is like no actually she beat me. She’s the best.
Alex is looking over J’onn. She tells him to wake up soon. Then M’gann is there telling him he is needed and that the great fight is coming. Then she kisses him and he bolts awake. He asks about M’gann but Alex tells him she’s on Mars. He asks what happened and Alex says “everything.”
J’onn comes into the command center and Winn comes running over to hug papa bear. He tells them that they need to protect the people so they need to tone down the news.
Clark and Kara head over to talk to Cat. She is happy to see Clark and she wants him to James about the vigilante business. Kara is also there. Cat wants to know where the story is about the fight. They tell her that Supergirl wants the coverage to back off to save civilians. Then Cat asks Kara if Supergirl is ready and Kara says yes. Cat will bet on Supergirl.
On their way out, they get summoned to Lena’s office. She explains that the device was made to spread kryptonite in the earth’s atmosphere so the Supers couldn’t live there. She wants to use it to distribute non-toxic levels of lead instead to get rid of the Daxamites. All of them. Lena asks Supergirl if she knew Mon-El and Kara were dating. Supergirl tells her to get to work on the machine.
Back at the DEO, they explain the device to everyone and Mon-El plays the martyr. Kara is adamant she is going to win though so none of this will matter. J’onn sends Winn to help Lena and Kara and Clark go to spar.
They take about using love as a superpower and a motivation to fight for the right reasons. Then it’s time to head to the battle. They go over the terms of the fight “for the earth.” Rhea gets the planet. Kara gets to give the Daxamites the boot.
They are mid-battle when Rhea’s team starts bombing people. She doesn’t care about the sacred oath. She just wants to win. J’onn and Superman start sending out teams to help the other people. Mon-El leaves the fight to “be a hero” and Alex is in charge of the DEO.
Turns out there is kryptonite in Rhea’s blood. Every hit Kara lands will weaken her. Meanwhile, Lena and Winn finish their device but only Supergirl can activate it. Cat and James are at CatCo when Superman and a Daxam fight come in.
M’gann turns up with a bunch of Martian reinforcements. It’s too much though. Alex calls Supergirl to say that they are going to lose. Supergirl apologizes to her boyfriend and then activates the device. The troops flee and Rhea dies. Dude is having trouble breathing and Kara begs Alex for a solution. She comes up with one on her own. She sends him off to space in a pod with her necklace from her mother. They cry. No one else does though.
Everyone is cheering. They win. Kara is standing on a balcony alone when Clark comes out to say his goodbyes. He’s humbled by her. She’s stronger than he ever will be.
J’onn and M’gann talk about her army. She tells him that she heard his mind cry out. She kisses him and he asks her to stay. She says for a while.
Alex goes out to talk to Kara. She tells her how proud she is of her and offers to stay with her. Kara tells her to be with Maggie. She needs to know that they are happy and tells Alex to never let her go. Kara takes off and Maggie comes out. She tells Alex that Kara will be okay. ALEX PROPOSES! And it’s amazing and wonderful and Maggie smiles with dimples and all.
Kara goes to CatCo and talks to Cat about how she had a boyfriend and it didn’t work and it hurts like hell and everyone close to her is in a happy relationship and she thought she could have one too. Cat tells her that women are strong because they can be vulnerable and she can soar above this and prevail. Kara remembers something she has to do and as she leaves Cat calls her Supergirl.
The thing she has to do is fly away crying. Mon-El is still alive in space playing with the necklace.
There is an epilogue of the day Krypton fell. Clark gets shipped off. Then Kara. Then on some bad guy planet, the next season villains smear blood on a baby’s head and send it out into space.
So we are supposed to care about him being in space. I get that. I don’t though. Did James even talk in this episode? I was happy to see M’gann back too. Also, this is very devils advocate but… Maggie didn’t say yes did she? Like this probably won’t actually work out the way people want it to. That sucks.