, James, Winn, Alex, Eliza and Mon-El celebrate Thanksgiving. Alex intends on coming out to Eliza, while James and Winn debate revealing the truth about Guardian. A mysterious interdimensional portal opens over the table. J'onn intends to discover Cadmus's plan with Kara's blood. Kara visits Lena Luthor to discern what she knows about her mother, Lillian Luthor, and Cadmus. Lena alerts Lillian that a reporter is raising suspicions about her. Hank Henshaw plants a device that unleashes smoke at the bar, which kills all the aliens inside except for Mon-El. Mon-El is placed in isolation and Eliza is brought in to figure out the toxin. The virus consumes Mon-El before Eliza determines it is Kryptonian. Kara determines Cadmus needed her blood so Henshaw could break into the Fortress of Solitude. Kelex regards Kara as an intruder and attacks; she learns Henshaw accessed the file on Medusa, a virus created for defense against potential invaders by her father. Eliza affirms her support for Alex coming out. Kara confesses to J'onn her feelings about her father's involvement in Medusa and he divulges that he is turning into a White Martian. The isotope Cadmus needs to weaponize the virus is only found at L-Corp. Kara and Henshaw battle in the lobby of L-Corp. The police arrive and he injures Maggie Sawyer; the portal reemerges and keeps him from stealing the isotope. J'onn and Winn are not convinced Lena is different than Lillian, so Supergirl tells Lena about her mother being Cadmus' leader. Lena accuses her of continuing Superman's witch hunt against the Luthors. Mon-El tells Kara that Eliza thinks he is dying and he kisses her as she admits that Medusa is her family's fault. Lena confronts Lillian about Cadmus and gives her the isotope. Winn traces it to National City's port, where Supergirl tries to convince Lena to not release the missile, but Lena launches it. Supergirl races after the missile while J'onn battles Henshaw. In their battle J'onn transforms into a hybrid Green/White Martian and gains the upper hand. The missile explodes, but has no effect, as Lena previously rendered the virus inert after double-crossing Lillian. Lillian is arrested but Henshaw escapes. An alien ship is looking for Mon-El and any Daxamites throughout space. Mon-El is cured and Eliza reverse-engineers Medusa to restore J'onn's Green Martian cells. Maggie admits she reciprocates Alex's feelings. Barry Allen and Cisco Ramon arrive at Kara's via the portal; surprised, Kara is ready when Barry asks for help with a problem on their Earth.
The episode ends with a scene setting up the crossover event "Invasion!" that begins on The Flash season 3 episode 8, continues on Arrow season 5 episode 8 and concludes on Legends of Tomorrowseason 2episode 7. This scene is later repeated in the Flash episode of the crossover. Kara/Supergirl appears in all three episodes as a visitor to their universe due to Supergirl being set in a different Earth, referred to as Earth-38 by the inhabitants of the Arrowverse, and has been informally referred to as "Earth-CBS" by Arrow showrunner Marc Guggenheim, named for the network where Supergirl first aired.
Reception
Ratings
The episode attracted 721,000 viewers for its British premiere, making it the 4th most watched programme on Sky One for the week.
Critical response
This episode received good reviews. Caroline Siede of The A.V. Club gave the episode a B. Cliff Wheatley of IGN gave the episode an 8.4/10, stating "Supergirl wrapped up the first half of Season 2 on solid footing. This episode mostly avoided the disappointing Guardian subplot in favor of bringing the show's more important plot threats to a temporary conclusion. Between the enjoyable Kara/Mon-El romance, the conflict with Lillian Luthor and the battles with Hank Henshaw, there was plenty to enjoy in this mid-season finale. Unless, that is, you were tuning in specifically because of the crossover connections."
