Supergirl realizes that in order to stop Lex and Leviathan she must work with the one person she never thought she'd trust again – Lena. Nia keeps dreaming about Brainy but struggles with what the dreams are trying to tell her. Meanwhile, Brainy realizes there is only one way to stop Lex.
Lex proceeds to lay an intricate plan to bring Lena closer to him, defeat Leviathan's latest attack, and pit Supergirl and team against Leviathan. It is also revealed how Lex came into power after Crisis.
Lex tasks Supergirl with protecting Andrea from an anti-tech extremist, but his nefarious purpose goes beyond merely keeping Andrea alive. Meanwhile, Lena moves forward with Non Nocere, with Lex's help.
The Monitor sends Harbinger to gather the worlds' greatest heroes - Supergirl, The Flash, Green Arrow, Batwoman, White Canary, The Atom and Superman - in preparation for the impending Crisis. With their worlds in imminent danger, the superheroes suit up for battle while J'onn and Alex recruit Lena to help them find a way to save the people of Earth-38.
Kara and William team up on an investigation that exposes a terrorist plot on the eve of the worldwide launch of Andrea Rojas's VR contact lenses. Meanwhile, Kelly and Alex celebrate an anniversary, but Alex's safety is in jeopardy.
Kara's investigation into William Dey's "criminal" activities results in a shocking revelation: He is not who she thinks. Meanwhile, the conflict between Malefic and J'onn J'onzz reaches a boiling point.
In the Season 5 premiere, Kara is surprised to find that CatCo has a new owner who has brought in a star reporter. New couples emerge and explore their budding relationships while J'onn J'onzz receives an unexpected visitor.