Martin and Ronnie return to S.T.A.R. Labs to help the team as Barry must make a life-changing decision thanks to Harrison's machinations.
Barry turns to Captain Cold for help when Harrison's plans threatens the imprisoned metahumans. Meanwhile, Iris makes a decision concerning herself and Eddie after the team rescues the officer from Harrison's underground base.moreless
Reverse Flash unleashes Grodd on Central City as a distraction from his own plans, and the telepathic gorilla abducts Joe.
Barry and the others manage to access Cisco's visions and try to recreate the conditions where Harrison confessed to Nora's murder in the original timeline. Meanwhile, Eddie asks a favor of Joe but is surprised at his partner's refusal.moreless
While Joe and Cisco take a road trip to Starling City to find evidence confirming Harrison's guilt, Flash deals with Everyman, a metahuman who can take the shape of anyone he touches.
Two scientists fall victim to killer bee attacks, and Barry's friends figure that a metahuman is responsible. Meanwhile, Felicity and Ray come to Central City to recruit Cisco's help in repairing Ray's Atom suit, and Ray offers to help. Meanwhile, Iris suspects that Eddie is keeping something from her and demands answers.moreless
A new terrorist calling himself Trickster launches an attack on Central City, and Joe and Barry reluctantly meet with the original Trickster, imprisoned for 20 years after a homicidal rampage. Meanwhile, in the past the events leading up to Harrison becoming Reverse Flash are revealed.moreless
Mark Mardon, Clyde's brother, recovers from his injuries and comes looking for Joe, the man who killed his brother. As Flash tries to cope with Mark's weather control powers, Cisco discovers the truth about Reverse Flash.moreless
After the nuclear explosion outside of Central City, Eiling comes after Firestorm, intent on using him to develop super-soldiers. Meanwhile, Mason asks Iris to help him investigate S.T.A.R. Labs, and Martin and Barry discuss the possibility of time travel after Joe shows Barry what he found at the old house.moreless
When the merged Martin and Ronnie attack a physicist, the team sets out to bring in "Firestorm". Meanwhile Joe recruits Cisco to help him investigate the house where Nora was murdered.
Barry and Caitlin go looking for new love, but only Barry is successful when he meets a sports reporter. Meanwhile, Cisco considers a surprising offer, the team take on a teleporting metahuman, and Henry is injured at Iron Heights.moreless
Hartley Rathaway, a former S.T.A.R. Labs scientist who tried to warn Harrison about the generator, comes back looking for revenge. While he launches a wave of sonic-based attacks, Iris gets a new job, and Joe has Eddie secretly investigate Harrison.moreless
Captain Cold recruits a partner to take on Flash and dispose of the hero once and for all. However, when Barry chooses to focus on his rematch with Reverse-Flash, the villains take Caitlin hostage to force the speedster's hand. Meanwhile, Iris prepares to move out, and Cisco tries to redeem S.T.A.R. Lab's reputation.moreless
Barry finds the man who killed his mother, but soon discovers that his opponent is faster than he can imagine. He turns to Joe and Harrison for help trapping his opponent, but things don't go as planned. Meanwhile, Caitlin discovers that Ronnie is alive and enlists Cisco's help to find him, and Eddie asks Iris to move in with him.moreless
Oliver, Felicity, and Diggle come to Central City to track down a boomerang used in a murder, and team up with Barry. However, when Barry falls under the influence of a villain who puts him into a fit of rage, Oliver must battle his friend before he kills someone. Meanwhile, Eddie tries to form an anti-Flash task force when he believes that the speedster poses a danger to the city.moreless
The Flash loses his powers while battling Farooq, a metahuman who can drain electricity from power systems and human beings alike. . Meanwhile, the Clock King--William Tockman--escapes during a prisoner transfer and takes Joe and Iris hostage.moreless
Flash battles a new metahuman, Tony, who can turn into superstrong steel at will. Things become personal when Barry realizes that Tony is the boy who bullied him in high school... and now he's abducted Iris. Meanwhile, Joe asks Harrison to help him investigate Nora's murder, but the scientist soon realizes that Joe considers him a suspect.moreless
General Wade Eiling takes over the police investigation of a thief who uses explosives, and Barry soon discovers that the thief is a metahuman who detonates anything that she touches. Meanwhile, Joe asks Barry to convince Iris to stop writing her blog about the Streak.moreless
Career criminal Leonard "Len" Snart acquires a cold gun stolen from S.T.A.R. Labs and goes after a rare diamond... intent on stopping Flash cold after an earlier defeat. Meanwhile, Felicity comes to town to check on Barry, and Joe continues to give Iris and Eddie the cold shoulder after he learns that they're dating.moreless
A metahuman killer goes after his enemies using his ability transform into poison gas. Meanwhile, Caitlin revisits the site where her fiancé Ronnie died, and Joe visits Henry in prison.
Barry tries to take on six gunmen robbing a university award ceremony, but inexplicably passes out. While the S.T.A.R. scientist try to find out what's wrong with him, Iris becomes intrigued by the "red streak."moreless
In the series finale, the Department of Defense's closure of Eureka is delayed by random wormhole materializations.
The doubles steadily take over GD, which means Fargo, Allison and Zane are in a fight for their lives and everyone else's as they try to avoid capture and fix the problem.
The Department of Justice arrives to investigate Grace, and Henry struggles with his conscience. Holly receives a message that triggers a chain of events. The question is whether it's her actions or Fargo's malfunctioning signature achievement that are causing the scary incidents all over GD and the town.moreless
Carter and Allison's perfect honeymoon is interrupted when sabotage is discovered in Eureka. Elsewhere, Holly faces another hurdle to remain intact.
While under the influence of a smart drug, Carter becomes a genius like everyone else in town and starts to change the laws of physics. Unfortunately, his condition soon endangers all of Eureka, including Allison's brother who is in town just to meet his new brother-in-law.moreless
Carter and Allison's romantic plans run afoul of a rogue submarine, and it's up to Jo to save their lives … if she can fix the mess at Global Dynamics caused by an out-of-control prankster in time.moreless
The Department of Defense insists on installing new security and removing all Astraeus artifacts, but Fargo resists because he believes Holly is alive in the matrix. Elsewhere, Henry recruits Carter for a brain experiment.moreless
When the ship with the Astraeus crew returns to earth, its occupants discover that four years have elapsed and time isn't the only thing that has changed.
As Carter and Blake prepare a Christmas surprise for the kids, a wave of energy sweeps over Eureka, transforming everyone into animated characters.