James and Winn want to tell Kara their secret, but Alex tells them no because she has her own secret to share. She gets interrupted before she can come out to her mother.
Kara plans to use her reporting skills and sneakiness to find out what Lena knows about Lillian's plans.
Cyborg Superman sets off a gas bomb inside the alien bar killing all of the aliens. Mon-El is put into quarantine at the DEO in case he's been exposed. J'onn insists he and Kara stay in the DEO until the toxin is identified as well. Alex brings Eliza in to help.
Mon-El collapses from the virus, but it turns out he can't infect other aliens. Eliza determines the virus is from Krypton and Kara realizes her blood was used to get into the Fortress of Solitude.
Kara learns the virus was created by her father to protect Krypton.
Kara battles Cyborg Superman at LCorp. Maggie arrives with back up and she's injured.
Supergirl tells Lena her mother is behind Cadmus and asks for her help finding her. Lena refuses.
Kara visits Mon-El's bedside and he kisses her.
Kara and J'onn go to stop Lillian and Lena from unleashing Medusa on the city. Lena sabotages her mother's plan and turns her in to the police.
Eliza finds a cure for Mon-El and is able to turn J'onn back into a Green Martian.
Maggie tells Alex that life is too short and kisses her.
Barry and Cisco arrive in Kara's apartment. Barry tells her he needs her help.