In 2001, Barry Allen witnesses his mother, Nora, being murdered, and his father, Henry, is blamed, despite Barry's claims that a man inside a blur is the real murderer.
In 2014, Barry returns to Central City after his trip to Starling City. His legal guardian, Detective Joe West, and his partner, Detective Fred Chyre, are investigating another bank robbery committed by Clyde Mardon and his brother, Mark, notorious outlaws recently released from Iron Heights. Barry identifies their getaway vehicle and finds evidence that they're hiding in a farm.
Barry and Iris West later go to S.T.A.R. Labs to see the Particle Accelerator being activated. Iris' purse is stolen, and Barry pursues the mugger, but is overpowered before the man is arrested by Detective Eddie Thawne, a recent transfer from Keystone City whom Detective West dislikes.
West and Chyre find the Mardons' hideout, and Chyre is killed by Clyde, who then boards a plane and leaves with Mark. Suddenly, the Particle Accelerator explodes and destroys the plane. Barry returns to his laboratory after failing to impress Iris, and is struck by lightning.
9 months later, Barry wakes up at S.T.A.R. Labs and meets Cisco Ramon, Caitlin Snow and Harrison Wells. He visits Iris to tell her he's back, and begins to experience the side effects of his super-speed. After testing his limits in a Ferris Aircraft air strip, Barry visits Iris again, and finds out she's secretly dating Eddie. Meanwhile, Clyde has survived the explosion and can control the weather, which he's using to rob banks. West and Eddie, his new partner, are investigating the robberies, but have no leads.
Barry and Iris are talking when Clyde drives by them after robbing another bank. Barry runs after him and forces his car to flip, but Clyde summons some fog to escape. Barry tells West that Clyde is alive and can control the weather, but West doesn't believe him, and they get into a fight, with West claiming Barry has to stop chasing the impossible and accept his father murdered his mother.
Barry returns to S.T.A.R. Labs and confronts Wells, who admits that the explosion breaching their dimension, releasing unknown energies into Central City, and that they might have created other superpowered "Metahumans" such as Barry. Wells refuses to help Barry stop Clyde, claiming Barry's powers are his only chance to salvage S.T.A.R. Labs, and he can't risk it.
Barry goes to Starling City to seek advice from Oliver Queen. Oliver assures Barry he can be more than a vigilante, and inspire the people in a way the Arrow can't. Uplifted, Barry returns to Central City and asks Cisco and Caitlin for help to stop the Metahumans. Cisco gives him an experimental, abrasion-resistant suit, and Barry springs into action.
After a sketch from one of the victims proves that Clyde is alive, West and Eddie go to the old farm and find him there, claiming he's a god and will rule the world. Clyde begins summoning a massive tornado to destroy Central City when Barry arrives. Encouraged by Wells, who apologizes for his earlier actions, Barry manages to unravel the tornado and Clyde is then killed by West to protect Barry.
West finds out Barry's secret identity and is convinced of Henry's innocence. He makes Barry promise to not tell Iris his secret. Barry later visits Henry and tells him he might have found a lead to Nora's killer, and he'll do whatever it takes to bring him to justice and prove Henry's innocence. Henry just wants Barry to move on, and Barry claims that he finally can.
Barry begins fighting crime and protecting people as "The Flash". Meanwhile, Wells ventures into a secret room at S.T.A.R. Labs, revealing that he has been pretending to have been paralyzed in the explosion. He then accesses a holographic newspaper from 2024 announcing that a merger between Wayne Tech and Queen Consolidated is complete, that the red skies have vanished, and that the Flash has disappeared after the "Crisis".