Barry and Iris's wedding brings the gang together, but things go awry when villains from Earth-X attack the ceremony. All of the superheroes band together with help from their super friends like Citizen Cold, The Ray, Felicity Smoak, Iris West and Alex Danvers to take on their most formidable villains yet. Earth's mightiest heroes - Green Arrow, Supergirl, The Flash and White Canary - lead their teams into battle to save the world.

The crossover starts on Supergirl S03E08 Crisis on Earth-X (I), Arrow S06E08 Crisis on Earth-X (II) and The Flash S04E08 Crisis on Earth-X (III).

“Worlds lived, worlds died. Nothing will ever be the same.”

The crossover starts on Supergirl S05E09 Crisis on Infinite Earths: Part One (I), Batwoman S01E09 Crisis on Infinite Earths: Part Two (II), The Flash S06E09 Crisis on Infinite Earths: Part Three (III) and Arrow S08E08 Crisis on Infinite Earths: Part Four (IV)