Kara’s friends must find a way to save her life when a parasitic alien attaches itself to her and traps her in a dream world where her family is alive and her home planet was never destroyed. Also, Alex, Hank and the DEO must fend off a Kryptonian attack while Kara is out of commission.

Still reeling after learning about Lena’s secret, Supergirl asks Guardian for a favor that could alter his relationship with Lena forever. Meanwhile, with all three Worldkillers united, Supergirl and the team brace for an epic battle.

Supergirl, The Flash, Green Arrow and Superman engage in the battle of their lives.

The crossover starts on The Flash S05E09 Elseworlds (I) and Arrow S07E09 Elseworlds (II).

Lex Luthor descends upon Washington, DC and summons Lena and Lillian Luthor to the White House. Supergirl realizes she has one last chance to stop Lex and turns to the power of the press to help her.

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.

This crossover continues on Batwoman S1E09, The Flash S6E09, Arrow S8E08, and Legends of Tomorrow S05E01.

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 and the super friends take drastic action after a loved one is kidnapped by Nyxly and Lex. An unlikely ally steps in to help the team.

Supergirl is joined by familiar faces from the past to help her stop Lex and Nyxly for good. Meanwhile, Alex and Kelly prepare to walk down the aisle.