Barry has his hands full when he takes on a dangerous meta who can control technology, while also confronting an obstacle in his personal life: the ramifications of abandoning Iris for six months to balance the Speed Force. Meanwhile, Gypsy breaches in for a hot date with Cisco, but she gets annoyed when his work keeps them apart.

Cisco is shocked when Gypsy's father, Breacher, shows up on Earth-1. Breacher takes an immediate disliking to Cisco and decides to hunt him. Meanwhile, Barry runs into his old nemesis, Ralph Dibny.

When collectors of Native American artifacts are attacked by a meta named Mina Chayton who can bring inanimate objects to life, Barry turns to a surprising ally for help. Determined to crack the identity of The Thinker, Harry enlists Cisco's help to summon the ultimate think tank: "The Council of Wells'," a roundtable of the brightest Harrison Wells' from various Earths.

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) and Arrow S06E08 Crisis on Earth X (II). It continues on DC's Legends of Tomorrow S03E08 Crisis on Earth X (IV).

As Barry’s trial for the murder of Clifford DeVoe begins, Iris and Joe must decide how far they are willing to go to keep Barry out of prison.

A meta who can shrink anything he touches battles Team Flash. Cisco and Ralph get caught in his crossfire and are shrunk to miniature versions of themselves. Cecile realizes her pregnancy has caused her to have temporary powers and discovers she can hear other people’s thoughts, which unnerves Joe. Meanwhile, Barry meets someone with a mysterious connection to Henry Allen.

Barry meets a powerful woman whose abilities could help him in his battle with DeVoe. Meanwhile, after learning that DeVoe is targeting everyone who was on the bus, Ralph decides he doesn't want to be a hero anymore, his only concern is staying alive. Harry offers to help Joe.

Team Flash confront a new bus meta, Matthew aka Melting Pot. He has the ability to swap people’s DNA, so during a battle with Team Flash, he transfers Barry’s super speed to Iris. Now, with a new threat unleashed on Central City, Barry must act as the team leader while Iris takes on the mantle of superhero speedster in order to defeat their new foe.

When Barry and Team Flash find a way to enter The Thinker’s lair, Ralph considers crossing a dangerous line to defeat DeVoe. Meanwhile, Joe is concerned by Harry’s recent behavior.

Barry and Team Flash team up with Gypsy to try to thwart Thinker's plan. Meanwhile, Cisco and Gypsy have a heart to heart talk about their relationship.

When DeVoe assaults an A.R.G.U.S. facility to complete his Enlightenment Machine, Barry realizes the only way he can stop him is if he allows Cisco and Caitlin to accompany him into the facility. Still shaken by Ralph’s death, Barry isn’t sure he wants to risk any more of his friends’ lives and considers taking on DeVoe solo.

As Barry helps his daughter, Nora, become a better speedster, he and Team Flash also track down a meta stealing high-tech weapons, only to cross paths with a new foe named Cicada, who is hunting the very same meta with nefarious intent.

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.

Caitlin, Barry and Cisco learn something new about Caitlin’s father. Meanwhile, Iris and Sherloque follow a clue about Cicada.

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.

While Nora grapples with the revelation that Thawne killed her grandmother, Team Flash must stop the formidable team-up of a newly sprung from jail Weather Witch and Silver Ghost, a new meta-tech villain who can control engines and motorized technology. Meanwhile, Caitlin and Cisco discuss creating a meta-human 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.

After Iris lands in serious danger, Nora races to save her mother. Barry puts the finishing touches on the metahuman cure, leaving Cisco with a rare night off so he decides to take Kamilla on a date.

With the meta-human cure ready to use, Barry and Team Flash must figure out a way to subdue Cicada long enough to take it. Killer Frost steps in to help with the plan. Meanwhile, Joe eases back into work, and Nora isn’t happy about the way her dad plans to stop Cicada.

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.

Barry continues to struggle with how he feels about Nora's betrayal. Brie Larvan, Joss Jackam and Peter Merkel return to Central City. Meanwhile, Cisco makes a bold decision.

Barry faces off with his oldest, and most formidable nemesis, Reverse Flash.

When an experiment to save Barry's speed backfires, Nash Wells searches for a way to save The Flash and comes up with a dangerous plan. Meanwhile, Iris makes a startling realization inside the Mirrorverse and Cecile faces off with Rosa Dillon.

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.

The Flash must deal with Abra Kadabra's sudden return to Central City. The villain is back with a vengeance and a score to settle. Meanwhile, Allegra deals with a tricky situation and Caitlin suspects something is off with Frost. Iris is forced to look at a dark moment in her past.

Cisco and Chester travel back in time and get stuck in 1998, repeating the same day over and over again. The key to returning home is at Chester's childhood home but he refuses to visit.

With Frost facing an unjust punishment for her past crimes, Caitlin goes to great lengths to save her sister. Meanwhile, Barry's efforts to protect Speed Force Nora lead to a shocking discovery.

Iris is pushed to the limit as she seeks to uncover the mysterious truth about Psych; Barry initiates a new training system, that could potentially backfire, with devastating consequences; Joe and Cisco make life-altering decisions.

Cisco and Kamilla tell the team they are leaving Central City. However, Barry, Iris and Caitlin don't have much time to digest the news because a new version of Rainbow Raider strikes and OG Team Flash must join together one final time to save the city.

When Ultraviolet returns to Central City, Allegra is determined to find her cousin and change her heart. Meanwhile, Joe finds evidence that Kristen Kramer may not be the good cop she appears to be.

John Diggle arrives in Central City with a weapon to help Barry stop the Godspeed War. Meanwhile, Allegra and Ultraviolet's new bond is put to the ultimate test, while Joe and Kristen Kramer are hunted by a former colleague of hers.

The Flash enlists a host of speedster allies, including Iris and his children from the future - Bart and Nora West-Allen - to end the speedster war and defeat a deadly new adversary: the villainous Godspeed.