Six months after the Flash and his friends stop the Singularity, Central City holds a rally in the speedster's honor. However, Barry doesn't want to go given the sacrifice that was made by the true hero. Meanwhile, a new metahuman, Atom Smasher, sets out to kill the Flash.
The team's visitor, Jay Garrick, explains that he comes from a parallel world and was a speedster there, but lost his powers transitioning over. Now he insists that Barry needs his help fighting a new metahuman, Sand Demon, who came from Jay's world. Meanwhile, Officer Patty Spivot tries to join Joe's Metahuman Taskforce.
Lisa Snart, aka Golden Glider, comes to the team for help when her brother Captain Cold is kidnapped. However, the Flash soon discovers that the villain is working for his father Lewis, who has some mysterious hold over him. Meanwhile, Caitlin and Jay work together to build a speed cannon so that Jay can return to Earth-2, and Joe tells Iris the truth about her mother.
Martin begins to destabilize without Ronnie to merge with him, and the team desperately seek out another metahuman with similar abilities. They find two men: Henry Hewitt and Jefferson "Jax" Jackson. Meanwhile, Iris does some digging into Francine's past, and Barry is hesitate to become involved with Patty after what happened between him and Iris.
Barry battles another breacher, Doctor Light... and discovers that she's Linda's evil counterpart. Meanwhile, the team deals with a new Harrison Wells in their midst, and Barry asks Patty out on a date.
After Dr. Light escapes from her pipeline cell, Barry asks Linda to help them lure Zoom to their world. Meanwhile, the team questions Harrison's motives and Cisco tries to use his powers on the Earth-2 visitor.
While Harrison tells the team that he's heading back to Earth 2 now that they've failed to stop Zoom, Grodd launches a new series of attacks in an attempt to gain the chemicals that he needs to augment his intelligence. Meanwhile, Barry deals with his loss of self-confidence after Zoom cripples him, and Iris calls in a familiar face to help.
Barry and Cisco take Kendra to Oliver and his team, looking for protection when a mysterious immortal comes seeking Kendra. However, a figure from her past arrives to tell her the truth. Meanwhile, Jay refuses to help Harrison test his new speed-enhancement serum, Velocity-6.
Weather Wizard frees Captain Cold and Trickster from prison to help him get revenge on the Flash, but Cold has second thoughts. Meanwhile, iris tells Joe about the son he never knew he had, and Patty confronts the man who killed her father.
The Flash and his friends go up against a new meta-human, the Turtle. Meanwhile, Caitlin discovers the source of Jay's problems, and Patty questions whether she and Barry can have a relationship.
Eobard Thawne--Reverse-Flash--kidnaps Dr. McGee and forces her to find a way to send him back to his own time. Flash and his friends discover that Reverse-Flash is from a timeline before he killed Barry's mother, and realize that they may have no choice but to send him back. Meanwhile, Harry and Cisco work to stabilize Cisco's vibe power, and Caitlin desperately tries to find a cure for Jay's illness.
While Flash takes on a new meta, dubbed Tar Pit, Barry offers to help Harry come up with a way to seal the breaches. He's unaware that Harry has secretly siphoned off some of Barry's speed... and plans to remove the rest.
Barry and Cisco travel to Earth-2 with Harry to rescue his daughter, and discover a strange world where friends are enemies and enemies are even worse. Meanwhile, Caitlin help Jay regain his speed so that he can deal with a new metahuman menace, Geomancer.
While Cisco and Harry go looking for a captive Barry, Barry makes contact with the masked prisoner and learns that he is connected with Jay. Meanwhile, On Earth-1, Caitlin perfects Velocity-9 so that Jay can go up against Geomancer before he brings Central City down.
King Shark escapes from ARGUS captivity and makes his way to Central City to kill the Flash. However, the hero and his friends are preoccupied with the recent death of one of their own. Meanwhile, Wally resents Barry's presence in his family.
A new speedster arrives in Central City and spreads chaos wherever she goes. Flash takes the blame, and Iris' editor plans to write an expose on the hero. Meanwhile, Jesse discovers how far her father will go to protect her.
When Barry reaches a dead end in going faster, he decides to travel into the past and trick Eobard Thawne--posing as Harrison Wells--into showing him how to go faster. However, something, in the timestream follows Barry back... and it's not friendly.
With Harry's help, Barry becomes fast enough to stop Zoom. Using Vibe's powers, the team contacts Zoom on the other Earth and use his past to trap him. But Zoom manages to escape their trap and takes one of them hostage to force Barry to give up his speed.
Barry tries to cope with a life without superspeed, but finds himself forced to don the Flash suit when a metahuman abducts Harry believing that he's Harrison Wells. Meanwhile, Wally asks Joe to arrange a meeting for him with Flash, and Caitlin tries to escape her captivity.
Zoom begins his reign of terror, unleashing the Earth Two version of Cisco's brother Dante on the populace. Meanwhile, Barry debates whether to undergo the dangerous process Harry has created to give him back his speed.
While Barry is trapped in the Speed Force, his friends desperately try to bring him home... only to discover that he may not want to leave. Meanwhile, the particle experiment reanimates one of the team's old foes, who is obsessed with finding Iris.
The Earth Two metahumans attack Central City en masse, and Barry is oddly confident that the team can handle them. Meanwhile, Cisco has vibes of an ominous future, and meets the Earth Two counterpart of a woman he loved.
The team discovers what Zoom is up to, and why he wants Barry to race him. When they realize that Barry is out of control after the death of someone close to him, they lock Barry up for his own safety rather than let him participate in a race he can't win.