This week on Supergirl, the Flash appears in National City and helps Kara fight Livewire and the Silver Banshee, formerly Siobhan, in exchange for help finding his way home.
The DEO tests Siobhan to see how her scream saved her from falling off the top of the Cat Co. Media building. The doctor says she’s human. She doesn’t know how Siobhan did it. Siobhan hears a screeching sound and storms out. On her way through the halls, she hears Livewire say she wants to kill Cat and Supergirl.
Cat tells Kara that if she doesn’t snatch James up, someone else will. She says Kara needs to make him jealous.
Siobhan hears screeching and sees the face of a creature in her mind. She comes to Cat Co. and tells Kara she ruined her life. Siobhan screams, knocking Kara out the window. As she plummets towards the ground, Kara is saved by the Flash.
Kara tells the Flash that she needs to get back to the city and flies off. He follows below her at top speed causing her to stop. Neither of them has heard of the other. He realizes that he’s from an alternate Earth. He introduces himself as Barry Allen and asks for her help.
Kara takes Barry to the secret office at Cat Co. Media. Barry introduces himself to Winn and James. Winn is impressed that the theory of the multiverse is true. Barry explains how if you move fast enough, you can travel between the various versions of Earth. James is jealous that Kara is bonding with another man.
Cat meets Barry and tells Kara she wants her exclusive information about the new superhero that saved her. She tells James she needs a photo. When the guys leave the room, Cat congratulates Kara on making James jealous.
Siobhan goes to her aunt for help. Her aunt tells her about the banshee that cursed their family. The curse is triggered when someone wrongs them. She has to kill the person who wronged her to stop it or the power will grow, but her soul will be destroyed. She decides to partner up to kill Kara.
Siobhan uses her screech to break Livewire out of the DEO. Lucy calls Kara to warn her. Kara tries to convince Cat to escape, but she refuses. She says she has faith in Supergirl. Kara goes to Barry for help. She promises she’ll help him return home afterward.
Kara takes Barry to the DEO. He also works as a CSI, so Kara shows him to her sister’s crime lab.
Siobhan lures Livewire to an abandoned warehouse. She demonstrates her power and asks to team up against Cat, Kara and Supergirl.
Lucy tells James not to hold back with Kara because of her. They were never going to work.
Barry uses an algorithm to track Livewire’s energy to the warehouse. He asks Kara what her plan is, but she doesn’t have one. She just wants to catch the bad guys.
The Flash tries to shock Livewire with a buildup of energy, but ends up making her stronger. She shocks him. When Supergirl tries to attack, Siobhan appears as the Silver Banshee and makes her eardrums bleed with her scream. Kara and Barry fight back but eventually fly away because there’s no way to beat them.
Kara apologizes and Barry tells her that superheroes need to be prepared for the unexpected. She tells him why the city distrusts her. He says time will heal her relationship with the people.
Cat looks for Kara, but she’s at the DEO. Livewire and the Silver Banshee appear at the office. Winn tries to convince Siobhan to stop, but she attacks him then kidnaps Cat.
Barry makes special earplugs for himself and Kara to battle Siobhan. Livewire tells Supergirl to come to National City Park to save Cat. Supergirl brings the Flash.
Cat begs Livewire not to take away her sons’ mother. Siobhan attacks Kara and Barry, but their earplugs block her effect on them. Kara lets Cat loose. Livewire attacks a helicopter, but Kara saves the passengers and all the people below by blocking the lightning with her body. The people below are so taken with how Kara saved them that they attack Livewire and Siobhan. The firefighters shoot Livewire with their hose taking her down. The resulting lightning takes Siobhan down as well.
The news announces Supergirl as a hero again. Kara tells James that Barry helped the police come up with a way to lock up metahumans so they can get a fair trial.
Kara asks Cat if she can see Barry off. Cat knows he was the Flash and tells her to go.
Kara and Barry combine speed to send him home through the dimensional barrier. Before he leaves, he tells her that she should speed things up with James.
Kara calls James to her apartment. She makes a move and kisses him. He becomes rigid and walks out. Kara looks out the window and sees every human walking in the same direction. Non has activated Myriad against National City.