Medusa (1)

Plot:

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. Part 1 - Supergirl - S02E08 Part 2 - The Flash - S03E08 Part 3 - Arrow - S05E08 Part 4 - DC's Legends of Tomorrow - S02E07