Barry and Team Flash come up with a plan to stop Cicada. However, the plan calls for Barry and Nora to travel back in time to gather some key necessities. However, Barry hesitates, concerned about his daughter seeing certain parts of his life. Meanwhile, Sherloque takes his concerns about Nora to Iris, and Caitlin turns up a key asset in the fight against Cicada.

When Barry Allen and Oliver Queen wake up one morning and realize they have swapped bodies with each other, the two set off to find out what disturbed the timeline to cause such a shift. However, things quickly go from bad to worse when they present their case to Team Flash and the gang doesn’t believe them. Barry and Oliver realize they need Supergirl’s help and travel to Smallville on Earth-38 where they end up meeting Kara’s cousin, Clark Kent, and intrepid reporter, Lois Lane.

The crossover continues on Arrow S07E09 Elseworlds (II) and Supergirl S04E09 Elseworlds (III).

While Barry and Iris deal with the heartbreaking loss of their daughter, Nora, the team faces their greatest threat yet — one that threatens to destroy all of Central City. Meanwhile, Killer Frost has a brush with death that results in an unexpected new dynamic that will change her relationship with Caitlin forever.

Pariah enlists Black Lightning to help stop the Anti-Monitor after Flash-90 shares what he learned from his battle in ‘Elseworlds.’ With the help of Black Lightning, Barry, Cisco and Killer Frost come up with a plan that could save them all. Meanwhile, Iris has a heart-to-heart with Ryan Choi, while Oliver and Diggle return to an old familiar stomping ground.

The crossover starts on Supergirl S05E09 and Batwoman S01E09. It continues on Arrow S08E08 and Legends of Tomorrow S05E01.