The Legends travel back to the Old Wild West and gain the aid of a true legend, a morally ambiguous gunslinger with a penchant for danger, Jonah Hex, who has been battling outlaws and gangs and happens to know a thing or two about time travel. Hex warns the Legends to be extra careful in their journey to the small town of Salvation.

Being in the vicinity of the Time Masters leaves Rip and Rory incredibly disturbed for very different reasons. Meanwhile, Sara takes over the Waverider, Kendra is reunited with Carter and Snart decides he might be a hero after all.

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).