In the series premiere episode, Superman's cousin, Kara Zor-El -- after 12 years of keeping her powers a secret on Earth -- decides to finally embrace her superhuman abilities and become the hero she was always meant to be.

When Kara's attempts to help National City don't go according to plan, she must put aside the doubts that she -- and the city's media -- has about her abilities in order to capture an escapee from the Kryptonian prison, Fort Rozz. Also, Cat pressures James to use his connection to Superman to get her an interview with Supergirl.

Supergirl's powers are tested when Reactron (guest star CHRIS BROWNING), one of Superman's formidable enemies, arrives in National City and targets the young hero. Also, Cat plans to run an expose on Supergirl.

Kara's Thanksgiving may be ruined when she suspects her foster mother, Dr. Eliza Danvers (special guest star HELEN SLATER), who is coming to town, disapproves of her new role as a super hero. Also, when an accident transforms a volatile CatCo employee into the villainous Livewire, she targets Cat Grant and Supergirl. BRIT MORGAN guest stars as Leslie Willis/Livewire.

Kara's two identities are stretched thin when Supergirl must protect National City from a series of bombings and Kara is tasked with babysitting Cat's son, Carter (guest star LEVI MILLER). Also, James is conflicted when his ex-girlfriend Lucy Lane (recurring guest star JENNA DEWAN TATUM) seeks to rekindle their relationship.

Personal and professional stress get the better of Kara when she goes too far during a training exercise against Red Tornado, a military cyborg commissioned by Lucy Lane's father, General Sam Lane (guest star GLENN MORSHOWER). Also, Cat's tough exterior is shaken by a visit from her judgmental mother, Katherine (guest star JOAN JULIET BUCK), and Alex enlists Winn to look into her father's mysterious death. IDDO GOLDBERG guest stars as Red Tornado and its creator, Dr. T.O. Morrow.