As a powerful samurai threatens Central City Cisco recruits Caitlyn to try and get Barry out of the Speed Force. But the man who comes out is not the same as who Barry was when he went in.
Barry and Iris face new challenges to their relationship after Barry's return, while a meta who can control technology seeks revenge on those who have wronged him. Cisco finds it difficult to balance work and his personal life when Gypsy arrives for a date.
The team's luck takes a turn for the worse after Becky Sharpe gets a run of good luck, thanks to her exposure to dark matter. As the city descends into chaos, Harry Wells returns from Earth-2 with bad news for Wally.
The bus incident leads Joe and Barry to Ralph Dibny, once a corrupt cop who now suffers unusual effects from his exposure to dark matter. Cisco finds himself on the run after Gypsy's father shows up on Earth and is not impressed by the young man who is dating his daughter.
Iris's bachelorette party takes an unexpected turn when Amunet, the meta criminal Killer Frost once worked for, comes to reenlist Caitlin. Meanwhile Cisco, Joe, and Ralph take Barry out for a night on the town, as Joe contemplates the new challenge ahead for him and Cecile.
The Flash takes Ralph into the field on a mission to stop a meta who can bring inanimate objects to life, using them to attack collectors of Native American artifacts. Elsewhere Harry and Cisco summon the "Council of Wells" -- a group of brilliant Harrison Wells from around the multiverse -- to try and discover DeVoe's identity.
Barry becomes convinced that a local college professor is the Thinker, putting himself at risk to try and prove the truth. Meanwhile, Clifford DeVoe recalls the path that has made him what he is.
Supergirl finds herself captive of the invaders from a dark, parallel Earth, who wish to take her heart to save the life of one of their own. Meanwhile Oliver, Barry, and Earth's other heroes must escape a Nazi camp on Earth-X -- with help from that planet's own heroes Ray and Citizen Cold.
Amunet kidnaps Caitlin for her medical skills, demanding that she save the life of a young meta with telepathic abilities. Meanwhile the Thinker traps Barry in a speed-proof prison, forcing Iris and the team to decide which of their friends to try and rescue.
As Barry goes on trial for the murder of Clifford DeVoe, his family and friends try to convince him to disclose his secret identity to the court. Meanwhile Cisco and Harry must deal with an emerging meta who is unwittingly emitting deadly radiation.
With Barry in prison it's up to Ralph to protect Central City -- especially when the Trickster returns to wreak havoc alongside his mother, Prank. While Ralph must find the true hero inside himself, Barry meets a potential ally inside Iron Heights.
Team Flash goes in search of a meta with the power to shrink objects, only for Cisco and Ralph to get caught in his line of fire. Meanwhile Cecile realizes that her pregnancy has given her temporary powers of her own, and Barry tries to help a fellow prisoner who he's convinced was wrongfully convicted.
Barry decides to help the bus metas escape from Iron Heights when he learns that the warden is selling them off to Amunet. Elsewhere Ralph receives a visit from an old friend, and soon discovers that he has an ability he didn't know about.
After a nuclear bomb detonates in Central City the Flash turns to his speedster friends for help with the impossible task of stopping a devastating explosion that has already happened -- pushing themselves to the breaking point.
An encounter with a bus meta with the power to swap people's DNA leaves Iris infused with Barry's speed. While Iris takes on the speedster mantle to defend Central City, a de-powered Barry must adjust to his new role behind the desk at Star Labs. Meanwhile, Harry builds his own "Thinking Cap" to try and keep up with DeVoe.
Barry clashes with Ralph over his cavalier attitude toward their situation, as a new bus meta with the power to levitate objects starts a crime spree in Central City. Cisco faces a difficult task after Breacher arrives asking for his help, and DeVoe's wife grows suspicious of her husband.
The trail to the final bus meta leads Team Flash to a man able to live completely off the grid, giving them a chance to access DeVoe's secret lair. Joe grows concerned about the effect that Harry's thinking cap is having on him.
Needing to relocate the explosive metahuman Fallout to a safe location (but also avoid DeVoe anticipating their plan) the team recruits Leo Snart from Earth-X -- unaware that an enemy has followed him through. Harry tries to sideline Cisco's attempt to build a Thinking Cap of his own.
Team Flash calls on Gypsy for assistance after DeVoe begins stealing components of a device related to his endgame. Harry comes clean about his condition, and Marlize remembers the romantic early days of her life with Clifford.
Team Flash recruits the criminal meta Amunet Black in an attempt to shoot down the satellites DeVoe plans to launch into space, but must first do her a favor. When the Council of Wells refuses to help Harry he and Cisco convene a new group: the "Council of Harrisons."
After DeVoe assaults a high-security A.R.G.U.S. facility Barry must overcome his grief to train Cailin and Cisco for a risky rescue operation. Cecile's pregnancy powers take a surprising twist, and Iris and Harry attempt to recruit a key ally.
With Cecile in labor Team Flash uses her powers to send Barry inside the mind of the Thinker, hoping to draw out his good self in time to stop the cataclysm of the Enlightenment.
