Kara wakes to find herself on Krypton. Her mother is there, insisting she is recovering from a fever. She insists this is a dream, a hallucination; mom insists the fever still has her in its grips.
Cat is on the warpath, looking for Kara. Winn and James call Alex, and the three of them break into Kara’s apartment. They find her on the floor, an enormous mutant flower growing out of her chest. They rush her to the DEO, where it seems this organic organism has attached itself to Kara. Her brain activity is normal, but she has no response to external stimuli. They try to pry it off with a titanium claw, but it quickly becomes clear that doing so would kill Kara. Alex and Hank go pay a visit to Max, and Alex attacks him, convinced that he had a hand in this. Hank has to pull her off – he doesn’t think Max was involved.
No, this was all Non’s doing. The device is called a Black Mercy, and he assures Astra that this was his way of compromising. He didn’t kill Kara; she is at peace.
In her dream world, Kara is panicked and thinks she is being manipulated. But then she sees a sculpture she made for her dad, and the warm feelings arouse in her. Her conscious brain is fighting the urge to give in to the fantasy. She starts to forget the word “Earth.” Then her father shows up, and aunt Astra (before she was all evil) and even young cousin Kal-El. And just like that, she buys in to the fantasy.
Back in the real world, Kara’s absence has not gone unnoticed by Cat. Alex convinces Hank to take on Kara-form and take her place at work. Of course, it isn’t as easy as Hank assumes it will be – it even makes him miss his alien prison. This provides some cheap laughs but ultimately a nervous breakdown from “Kara” makes Cat give her the rest of the day off.
Alex returns to Kara’s apartment, looking for any clue that might help her. All she finds is Astra, who swears she is not there to fight. She explains to Alex that the Black Mercy has trapped Kara in her perfect fantasy life. She must reject that life herself or be forever consumed by it. She promises to help Alex if she will just trust her. Easier said than done, but Alex does, and Astra tells her how to fix it.
With a quick “the enemy of my enemy is my friend” speech, Alex convinces Max to help her. They need to modify the virtual reality so that Alex can enter Kara’s projection and convince her to come out. Before going in, Alex makes James promise that he won’t let Hank try to pull her out without Kara. “I come back with my sister, or not at all.”
Alex “wakes” on Krypton, and finds Kara with her mom, dad, and Kal-El. By now, Kara has bought into the fantasy and doesn’t recognize her sister. Alura knocks out Alex, which causes real-life Alex to seize. As predicted, Hank’s immediate response is to pull Alex out, but James won’t let him. “She will never forgive you if she loses Kara.” Hank steps back.
Alex finds herself in cuffs, sentenced to banishment in the Phantom Zone for being an alien spy. She begs Kara to listen, because deep down, Kara knows it isn’t real. Referring to Kara as “Supergirl” and “my sister” seems to rattle the memories back into Kara, who wants for this to be real – but knows it isn’t. She hugs her mother and thanks her, but Alura’s eyes turn black. “We will never let you leave!”
Alex wakes in the DEO, and when she sees Kara is still unconscious, she flips out, thinking the boys pulled her out just as she was about to rescue Kara. The guys insist she woke on her own. Suddenly the Black Mercy seems to dry up a bit, and slithers off Kara, onto the floor, where it kind of gives up. Kara wakes, unharmed physically, but emotionally scarred. She demands to know where Non is.
Meanwhile, back at their secret lair, Non is suspicious of Astra’s sudden disappearance. Astra won’t respond to questions about where she was, but she promises she is dedicated to bringing humanity to its knees.
Winn made himself useful at the DEO and found that Non and his crew were using a solar storm to hide the fact that they were using LordTech servers to send out hidden transmissions. The team rolls out to stop Non and Astra from infecting the remaining server farms.
Kara finds Non and beats the hell out of him, furious that he made her lose her family again. She insists she will protect Earth until her last breath. “Humanity is the disease,” Non says like a standard super villain, “and Myriad is the cure.” He escapes, but not before knocking down a massive satellite dish, one so huge Kara has a hard time keeping it from crashing to the ground.
Meanwhile, Alex has found Astra at another site, and they fight. But Alex believes that Astra’s heart is no longer in this war. She loves Kara, and had plenty of chances to kill both her and Alex. J’onn J’onzz shows up and gives Astra a good beating. Astra gets the upper hand and holds a weapon to J’onn’s neck, promising him a soldier’s death. Suddenly a glowing sword impales Astra. Alex has killed her. She calls for Kara, who rushes over in time to say goodbye to her aunt. Astra is pleased to see Kara’s sister brought her back from the clutches of the Black Mercy. She warns Kara that Non cannot be stopped; that it is already too late to stop Myriad. She dies before she can offer anything helpful. Hank takes the blame for killing Astra, explaining to Alex that she is Kara’s superhero and he didn’t want anything to change that.
Myriad is operational, but Hank was able to bring back one of the control boxes and sends it to the lab to figure out what the hell they are in for.