When a nuclear bomb detonates in downtown Central City, Barry, Jesse Quick and Jay Garrick slow down time by entering Flashtime. As everyone in the city is frozen, the three speedsters push themselves to the breaking point to save the city and everyone in it.

Barry and Iris face the ultimate parenting test when Team Flash battles Spin, a savvy millennial armed with meta tech, and a dangerous agenda for their daughter, Nora. Ralph is feeling defeated until an unlikely source issues a challenge to help boost his confidence.

While Nora grapples with unresolved anger over her father’s disappearance in the future, Barry and Team Flash must stop a powerful new meta, Weather Witch, from killing her own father, Weather Wizard.

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).

During a battle with Cicada, Nora is severely injured. Due to Cicada's dampening powers, Nora's speed healing isn't working, leaving Barry and Iris scared for their daughter's future. Upset about his injured child, The Flash is filled with rage and confronts Cicada in a brutal battle. Meanwhile, Killer Frost keeps interfering with Caitlin's work on the cure.

When Sherloque wants to use a memory machine on Barry and Nora to help gain access to Grace's memories, Nora panics, fearing her parents will find out the secrets she's been keeping from them. Nora secretly decides to use the machine on her own which ends in disaster after she gets trapped inside Grace's mind. Barry and Iris go in after their daughter and Iris is brokenhearted by what she finds. Meanwhile, Ralph tricks Cisco into going out for a night out on the town.