Myr'nn inadvertently causes psychic disturbances at the DEO; Supergirl must work with J'onn to contain the chaos; Mon-El begins training Kara in fighting techniques he's learned in the future.

The subsequent complications from the Crisis leave Supergirl to face a chaotic threat.

Mxyzptlk returns with a proposition for Kara – what if she could go back in time and tell Lena her secret before Lex did, would things turn out different? Looking back over key moments throughout the series, Kara must decide if she wants to change history to become friends with Lena again.

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.

Supergirl intervenes when a building in the Heights that was set aside for low income housing is suddenly at risk to be sold to a major corporation. Supergirl recruits Orlando to help her win over the city, but things go awry when Nyxly shows up. Meanwhile, Nia trains with her mother.

Supergirl continues to fight Nyxly for the remaining totems but after Nyxly kidnaps William, Supergirl realizes she needs to take a more proactive stance to keep National City safe. Meanwhile, Alex faces the biggest challenge of her life.