Medusa

"Medusa" is the eighth episode of the second season of Supergirl. The episode starts four-part crossover with the eighth episode of the third season of The Flash, eight episode of the fifth season of Arrow and seventh episode of DC's Legends of Tomorrow. It will air on November 28, 2016

Synopsis
Eliza comes to town to celebrate Thanksgiving with her daughters. Alex decides it’s time to come out to her mother; Kara is shocked when Eliza suggests Mon-El has feelings for her, and Winn and James consider telling Kara the truth about the Guardian. Meanwhile, CADMUS unleashes a virus that instantly kills any alien in the vicinity so Kara enlists an unexpected ally – Lena Luthor. The epic superhero crossover kicks off tonight when Barry Allen and Cisco Ramon seek Kara’s help with an alien invasion on their Earth.