Supergirl and Clark team up to stop a new threat emerging in National City; Alex feels left out while Kara's family stays in town; a pod comes crashing down to earth.
Supergirl is seriously hurt when a kryptonite-powered villain attacks National City; Superman blames Hank for the attack after discovering the kryptonite was stolen from the DEO; Kara meets her boss, Snapper Carr, on her first day at her new job.
Alex and Detective Sawyer investigate an attack on the president; Kara searches for a recently escaped alien she thinks is behind the assault.
While investigating the murder of an unregistered alien, Kara and Alex find an alien fight club run by Roulette; Hank tries to get to know M'Gann better; Supergirl begins to train Mon-El.
Supergirl battles a ruthless new gang with dangerous alien technology; the team discovers Cadmus is staffing the criminals for a secret mission; Mon-El gets a job as an intern at CatCo; Lena invites Kara to a fundraiser.
The Guardian comes to help after a parasite alien drains Supergirl's powers; Mon-El considers a new career; Alex copes with a new reality.
Guardian tries to clear his name after he's accused of a murder committed by another vigilante; while on a mission to rescue Mon-El, who was captured by CADMUS, Supergirl comes face to face with Cyborg Superman.
When Eliza visits for Thanksgiving, Alex decides to come out to her; Winn and James consider revealing the truth about the Guardian to Kara; Barry Allen and Cisco Ramon seek Kara's help with an alien invasion.
When Kara investigates the story of a missing woman, she and Mon-El end up being thrust through a portal to another planet where the downtrodden are sold as slaves.
Livewire seemingly breaks out of prison; Supergirl takes Mon-El with her when she sees Livewire attack the NCPD; James wants to come clean with Kara; M'Gann has a psychic attack.
Armek, a white Martian, descends on National City intent on taking M'gann back to Mars to face her punishment as a traitor.
After Metallo breaks out of prison and frees Lillian Luthor, Lena is arrested by the police and blamed for the escape; Alex introduces Maggie to the gang.
A magical imp shows up on Earth, and after declaring his love for Kara, begins to wreak havoc on National City; Alex and Maggie celebrate their first Valentine's Day together.
Alex and Kara are thrilled when Jeremiah Danvers is rescued from Cadmus, but things go awry when a suspicious Mon-El questions Jeremiah about his sudden return.
Alex searches for Jeremiah while Kara investigates a series of alien abductions; in an effort to get Snapper Carr to run a story that would help her stop Cadmus, Kara agrees to set up an interview between Snapper and Supergirl.
A new villain in National City puts Supergirl on high alert; Winn's girlfriend gets him in trouble with the law; Maggie tries unsuccessfully to help Winn; the Music Meister attacks Supergirl.
A large bounty on Supergirl draws aliens from all over to National City; Alex and Maggie run into Maggie's ex-girlfriend; Hank receives an interesting order from the president.
Lena's ex-boyfriend comes to National City to unveil his nano-technology breakthrough; Lena asks Kara to attend Jack's conference with her for support.
Alex gets kidnapped and her captor threatens to kill her unless Supergirl releases a notorious criminal from prison; Rhea has an interesting proposal for Lena.
It's up to Guardian to intervene when an alien that has telekinetic powers attacks National City; Rhea's plan escalates.
Supergirl struggles to decide whether or not to obey the president's orders regarding Rhea's latest actions; Cat Grant returns to National City.