After stopping a plane crash Kara Danvers embraces her Kryptonian powers, taking up her cousin's mantle as a hero to defend National City -- which has come under threat from alien prisoners who have escaped from the Phantom Zone.
Kara struggles with her lack of experience when it looks like her efforts in National City may be doing more harm than good, and Alex tries to begin training her to fight. Meanwhile a member of an alien insectoid race turns up at a chemical plant, and Cat pressures James to land her an interview with Supergirl.
One of Superman's powerful enemies, Reactron, targets Kara after learning about her relation to the Man of Steel. Meanwhile, Cat plans to run an exposé on Supergirl.
While her alter ego is charged with watching Cat's son Carter, Supergirl must stop a serial bomber who is attacking National City and threatening Maxwell Lord's new high-speed train line. James is uncertain when his old flame Lucy tries to rekindle their relationship.
An accident transforms an outspoken radio personality into the villainous Livewire, who can channel and even turn herself into electricity -- and who targets Cat and Supergirl. Kara's foster mother comes to visit for Thanksgiving, causing friction with Alex.
When General Sam Lane comes to National City Supergirl is asked to fight an experimental combat android to test its capabilities -- only to have "Red Tornado" go rogue and escape. Cat's judgmental mother visits, and Alex begins to look into her father's mysterious death.
An earthquake puts National City in grave peril just at a time when Supergirl has temporary lost her powers, forcing Kara to confront what being a hero really means. When the D.E.O. goes on lockdown, Alex is caught between an escaped alien prisoner and her mistrust of Director Henshaw.
Kara takes on her aunt when Astra calls her out, prompting Kara to remember Astra's final conflict with her mother before Krypton was destroyed. Meanwhile Cat rallies the troops after a data breach threatens to expose her secrets to the world.
After Astra's Kryptonian husband Non captures Hank, Kara tries to extract their whereabouts from her aunt. Meanwhile, Cat threatens Kara's job unless she can prove that she is not Supergirl.
Winn's villainous father, a mass murderer nicknamed the Toyman, breaks out of prison and tries to reconnect with his son. Meanwhile Cat offers Lucy Lane a job at CatCo, and Alex asks Hank to use his secret abilities to infiltrate Maxwell Lord's facility and learn what he is up to.
The arrival of an anti-alien Senator is followed by an attack by a vicious White Martian, the species J'onn reveals is responsible for the holocaust of his people. Cat is caught off balance when her estranged son Adam shows up, drawn by a letter actually written by Kara.
Supergirl must square off against her super-powered doppelganger, Bizarro, who Maxwell Lord has sent to destroy her. At the same time, she must decide whether she can pursue a relationship with Adam while still being a hero.
After Kara awakens back home on Krypton, her friends discover that she has been incapacitated by an alien organism -- the Black Mercy. While Alex and the D.E.O. desperately try to remove it, Hank is forced to impersonate Kara to save her job, but finds it harder than he thought to be Cat Grant's assistant.
The D.E.O. tracks Fort Rozz's former jailer, who is hunting escaped prisoners and dealing out his own summary justice. Meanwhile Kara and James clash over the D.E.O.'s prisoner, and Kara meets her latest competition: a new assistant hired by Cat Grant.
When National City is threatened by an alien super-computer who calls herself Indigo, Supergirl visits her cousin's Fortress of Solitude for intel. Kara decides to leave the D.E.O. and take on the threat by herself, while Lucy and James' relationship reaches a crossroads.
Kara is exposed to Red Kryptonite, stripping her of her inhibitions and turning her against her friends and loved ones. After Supergirl threatens her life, Cat speaks out to turn the city against its hero.
Interrogated by the government, J'onn J'onzz reveals the fate of Hank Henshaw and Jeremiah Danvers -- prompting Kara to reveal her secret to someone in order to save her loved ones. Meanwhile, Siobhan tries to get Kara fired.
Kara gains a new ally when The Flash, a super-fast speedster from a parallel universe, arrives and asks for her help getting home. But first the two must team up to stop Siobhan -- a.k.a. "Silver Banshee" -- when she breaks Livewire out of the D.E.O. and goes after Cat.
When Non and Indigo subject the city's entire population to mind control, Supergirl must rely on Cat and Maxwell Lord for help in stopping them from seizing control of the entire planet. J'onn and Alex determine to return to National City to help.
After Non sends Alex to kill her own sister Kara must free National City from the control of Myriad -- only to learn that her enemies are using the technology to wipe out all of humanity.
