Leviathan welcomes Lex Luthor into their inner sanctum, as the group plots to eliminate Supergirl once and for all. While her friends fight to protect her, Kara gets help from Lena — and Brainy decides the only way to save the planet is to sacrifice himself.

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DAVID HAREWOOD DIRECTED THIS PENULTIMATE EPISODE

Supergirl (Melissa Benoist) realizes that in order to stop Lex (guest star Jon Cryer) and Leviathan she must work with the one person she never thought she'd trust again - Lena (Katie McGrath). Nia (Nicole Maines) keeps dreaming about Brainy (Jesse Rath) but struggles with what the dreams are trying to tell her. Meanwhile, Brainy realizes there is only one way to stop Lex.

David Harewood directed the episode with story by Derek Simon and teleplay by Emilio Ortego Aldrich & Nicki Holcomb (#519).