The episode opens on Krypton, where Kara Zor-El narrates her origin, — starting with baby Superman being rocketed to Earth, which we see. She, she tells us, was sent to protect him. As a teenager, she’s boarded into a pod, and promises her parents not to fail them. She cries, hugs her mother good-bye and is rocketed away — but a shockwave from Krypton’ s destruction tossed her into the Phantom Zone for two 24 years, until she arrived on Earth, still 12 years old, and was greeted by Superman, who placed her with the Danvers family — scientists who he had once worked with, who looked suspiciously like a different Supergirl and Superman — and their daughter, Alex.
Kara decided to try and fit in, since Kal-El didn’t need her protection and Earth didn’t think she needed a new superhero. She now works for Catco, Cat Grant’s media empire, where one of her coworkers is Winn Schott, who believes in alien conspiracy theories and has a crush on Kara, who shoots him down for a movie because she has a date.
Cat comes in, complaining that somebody with bad cologne used her private elevator and criticizes everything from her latte to her mother, and asks Kara to prepare termination notices for the Tribune, one of her newspapers. Kara objects, saying that the Daily Planet hasn’t had to downsize, but Cat notes that Metropolis has Superman, who essentially keeps the Planet in business with his larger-than-life antics. She sends Kara to go check on her new layouts from the recently-hired art director.
When Kara goes to see him, it’s James Olsen, former Daily Planet photographer and pal to Superman, who encouraged him to move out to National City. He gives Kara his framed copy of the first real picture of Superman. He also flusters her a little bit by telling her that she looks a bit like Superman in the eyes.
Back at home, Kara has called Alex to help her pick out an outfit for her date, and while her sister picks the outfit, she complains that working for Catco is not fulfilling. Alex picks a shirt for her and leaves for her flight to Geneva, where she has a conference.
On her date, Kara isn’t having a great time anyway, and then overhears her date asking a waitress for her number with her super-hearing. A TV comes on and it seems Alex’s flight had engine failure after takeoff. Kara runs outside and, after a false start, leaps into the air to chase down the jet, just as a second engine catches fire. She saves it, landing the plane in the water and standing on the wing for just long enough that Alex sees her and somebody can get a crappy cell phone picture before taking off again.
At home, Kara watches news reporting on the “guardian angel” who saved the flight when Alex comes in and chastises her for using her powers in public. Kara doesn’t even notice at first due to her excitement about what comes next. Alex tells her that it isn’t safe for her to do anything like that ever again, and Kara tells her she should go, that she’s tired.
The next morning, the local news is asking who the mystery flying woman is. At work, Kara is a little disappointed when Winn criticizes her lack of a costume. In Cat’s office, she’s furious that nobody on staff has managed to get something. James comes in and tells Cat that if there’s any connection between the girl and Superman, she’ll be back. Cat says she wants the hero to save her newspaper, but she needs exclusive content and an interview. On the way, out, Jimmy reminds Kara that saving a plane was the first thing Superman did. Kara tells Winn that she needs to talk to him on the roof. When he gets there, she confesses to being the girl from the plane, and when he laughs at her, she dives off the roof and then flies back up and lands in front of him.
At a nearby diner, a man is digging his fingernails into the bar, watching reports about the hero. Outside, he climbs inside of a tanker truck and reveals a ridge on top of his head. The man, Vartox, was ordered to bring the plane down, and is now tasked by a man on a communication device with killing the girl, who they assume is Alura Zor-El’s daughter.
At home, Kara tries on two costumes — both without capes — before trying to stop a car chase and realizing that the cape helps with aerodynamics. She gets a cape and heads out to stop a bank robbery, the bullets bouncing off her as she does so, but the cape itself taking hits.
When she comes back, the new costume has a sturdier cape and the House of El’s coat of arms — the “S” shield.
She then responds to a four-alarm fire at Gates and Igle, but before she can get there she’s hit with a Kryptonite bullet, which takes her down in mid-flight. When she wakes up, she’s in a lab, handcuffed to a table with Hank Henshaw of the Department of Extranormal Operations (DEO) standing over her. Moments later, Alex joins them, removing the cuffs.
Henshaw explains that the DEO exists to protect Earth from extraterrestrial threats, including Kara. They have her ship in their custody and say Superman is the reason for their existence. He says that her arrival also brought Fort Roz, a maximum security prison in the Phantom Zone that followed her pod to Earth. When it crashed, the alien convicts all escaped.
Henshaw tells Kara they don’t want his help, and that he doesn’t even really trust Superman. Alex apologizes to Kara for lying to her for years, and Henshaw tells Alex that Kara is dangerous.
Back at work the next day, Kara gets off the elevator to news that Cat has named her Supergirl. She goes into object, saying that she doesn’t like “girl,” and shouldn’t it be “Superwoman?” Cat tells her she doesn’t care, because she considers herself a girl, and so it’s Kara’s own problem if she doesn’t like the name. She threatens to fire Kara, but Olsen comes in, offering Cat photos of Supergirl from the bank robbery’s security cameras.
Outside, she objects to James’ help, when she hears a message in her head on a frequency humans can’t hear. Vartox challenges her to meet him at a power plant, and Kara heads to the roof and takes off, landing there and trying to use her vision powers to look around, then her hearing to hear him coming — but he flies in fast and attacks her. After he makes a mysoginistic remark, he attacks her, revealing that Alura was the judge who put him away, so he wants to kill Kara. They fight briefly and he starts to get the upper hand, talking trash the whole time. She’s rescued when Alex flies in in a chopper, firing missiles at Vartox, who gets away anyway.
They take Kara back to the DEO, where they dig a piece of Vartox’s blade out of her arm. Henshaw mocks her, and Alex says the reason she didn’t want Kara to be a superhero is that she knew about Kara’s mother and her connection to the convicts. Kara is discouraged, saying that the world doesn’t need her and leaving.
That night, she’s sitting alone when Alex comes to see her. She stands outside Kara’s door and tells her that her family needs her. She brings a projection of Alura that was found in the pod. Her mother shows up and tells her to “be wise, be strong and always be true to yourself.” Kara cries, and asks Alex what to do now. Alex tells her to change, and the pair walk into the DEO, Kara in costume. Alex tells Henshaw that he has to work with Kara, or Alex will walk.
The DEO picks up a “unique nuclear thumbprint” on Vartox’s weapon, and they decide to go after him; Supergirl tells Henshaw she’s going to go stop him, and Henshaw reluctantly agrees to let her.
She stands in the highway, trashing Vartox’s truck, and the two fight again. This time, more prepared, she dispatches him while Alex exposits that she can make his axe explode at a certain heat. Eventually Kara gets close enough that Vartox tries to kill her with the axe, feigns surrender, and then uses heat vision to blow it up, taking him out in the process. Rather than surrender, he uses a fragment of his blade to kill himself. Back at the DEO, Henshaw still has no faith in Kara. Alex asks whether she was really just recruited because of her connection to Kara; Henshaw says yes, but her own skills are why she gets to stay.
After meeting briefly with Winn at work the next day, she asks James to lunch; he tells her to meet him on the roof. James says that he was moving out of Metropolis anyway, so Superman sent him to National City to watch out for Kara. He said Superman wanted her to choose her destiny for herself, but that he sent a cape made from his Kyptonian blanket. James says that both Superman and he is proud of her, then suggests she has a city to protect. She takes off into the air, and narrates that she’s here to protect the world, even though her cousin doesn’t need her.
The man Vartox had spoken to over his communication device meets with his general, who is revealed to look exactly like Kara’s mother — it’s her aunt, who wanted to lead Krypton, but will now lead Earth instead.