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.

As Iris receives word of a career milestone, Barry is suddenly nowhere to be found. In trying to get back home, Barry runs across many familiar faces. Khione continues to figure out her powers, and Chester works on a suit for Allegra.

Wells presents Barry with a life-changing choice. Dr. Martin Stein and Ronnie Raymond return to help the S.T.A.R. Labs team with this final fight.

Team Flash throws a surprise birthday party for Barry, but things go terribly awry when Ramsey Rosso crashes the festivities.

Mark Mardon, having survived his apparent death during the black-matter explosion, returns seeking revenge on Joe for the death of his brother Clyde... and has the same weather-manipulation powers as his deceased sibling.

As Barry Allen stands on the threshold of his impending death in Crisis, his convictions are tested when the monstrous Dr. Ramsey Rosso infects The Flash with a mysterious, hallucinogenic contagion. Meanwhile, reporter Iris West-Allen uncovers a vast conspiracy.

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).

Barry, Caitlin, Cisco and Joe set a trap for Wells. Cisco uses himself as prey which puts him in grave danger. Meanwhile, Eddie makes a decision regarding Iris, which leaves Joe a bit unsettled.

With only 24 hours left until Savitar murders Iris, Barry struggles to save the woman he loves and makes the choice to use any means necessary to do so. Realizing he has one option left to save her, The Flash turns to Captain Cold for help.

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.

When Barry suddenly gains the power of speed thinking, he attempts to use his new gift to save Iris. While Barry is thrilled with his new power, Cisco is hesitant to trust it. Meanwhile, Eva must face a shattering truth.

Barry is thrilled when Oliver, Felicity and Diggle come to Central City to investigate a case involving a deadly boomerang. The crossover continues on Arrow S03E08 The Brave and the Bold.

Barry enjoys the annual tradition of tree trimming and gift exchange with Joe and Iris. He gives Iris a touching gift, but the moment is interrupted by Eddie’s arrival.

When Harrison activates the particle accelerator, the team has no choice but to evacuate the five metahuman prisoners. Unfortunately, with time running out, Barry has no choice but to turn to Captain Cold for help. Meanwhile, Eddie escapes but has some surprising news for Iris.

Vandal Savage arrives in Central City and sets his sights on Kendra Saunders. After Vandal attacks Kendra and Cisco, they turn to Barry for help. Realizing how dangerous Vandal is, Barry takes Kendra to Star City and asks Oliver and team to hide her until he can figure out how to stop Vandal. However, things quickly go from bad to worse when a man with wings AKA Hawkman shows up and flies off with Kendra. Meanwhile, Harrison develops a serum to make Barry run faster and asks Jay to test it out. The crossover continues on Arrow S04E08 Legends of Yesterday (II).

After discovering that Nora is working with Thawne, Barry and Iris disagree about how to handle their daughter in the wake of this shocking news. Team Flash isn't sure they can trust Nora, so they go through her journal to find out exactly how she came to work alongside their greatest nemesis.

When a villain calling himself the Trickster runs rampant in Central City, Joe and Barry go to Iron Heights to talk with the original Trickster.

Joe and Cisco go to Starling City to ask Quentin Lance for his help investigating the site of Harrison's car accident 15 years ago and determining what really happened. Meanwhile, Eddie is framed for a shooting by a shapeshifing metahuman who can take on the appearance of anyone he touches.

After recent events, Barry decides it’s time to confront Zoom and comes up with a dangerous plan. Caitlin sides with Jay and deems it too dangerous for Barry to engage with the speed demon. However, Iris shows her support and brings forth a surprising ally. We see what Earth-2 Harrison Wells’ life was like before coming through the breech.

Barry, Wells and Cisco journey to Earth-2 to rescue Wells’ daughter, Jesse from Zoom. Barry is stunned when he runs into Earth-2 Iris and Joe, but nothing prepares him for meeting Killer Frost and Deathstorm. Meanwhile, back on Earth-1, Jay has to take over the Flash’s responsibilities when a meta-human nicknamed Geomancer attacks Central City.

While training with Barry, Wally starts to have visions of Savitar, which he hides from the team. A dangerous secret threatens Barry and Iris’ happiness.

Barry and the team meet Tracy Brand, a scientist, who may be the key to stopping Savitar. Unfortunately, Killer Frost is also after Tracy so Team Flash must battle their old friend, which proves to be particularly difficult for Cisco. Joe and Cecile’s relationship takes a big turn.

Barry comes face to face with DeVoe. Devoe's past is revealed through flashbacks. Meanwhile, Iris puts the final touches on the wedding, which is a week away.

After Zoom unleashes an army of Earth-2 meta-humans on Central City, Barry is shaken when he sees their leader is the Black Canary’s Earth-2 doppelganger, the Black Siren. Meanwhile, Wally takes to the streets to help The Flash stop the meta-humans, which worries Joe. Iris and Henry are concerned about Barry taking on Zoom.