>Barry Allen is a forensic analyst for the Central City Police Department. As a child, his mother was murdered, and his father was blamed. Barry became a cop to prove his innocence.
>After his mother's death, Barry was adopted by the Wests, parents of his childhood friend Iris West. Barry and Iris always had feelings for one another, but never acted out on them.
>Barry is called to investigate an unidentified woman found dead near the riverbank. He believes she might have been exposed to extremely low temperatures and requests a spectrometer analysis from Captain Fred Chyre, but is denied.
>Barry breaks into S.T.A.R. Labs to use their spectrometer, but is caught by a scientist, Valerie. She takes a liking to him and agrees to analyze the samples and send him the data.
>Barry goes to Iris' apartment and finds out she's engaged to a banker, Nathan Newbury. Iris has recently lost her job as an investigative reporter for the Central City Daily and becomes an independent blogger.
>Valerie sends Barry the data. While he's studying it, he's struck by lightning and thrown and bathed in chemical products. He awakens in S.T.A.R. Labs, and finds out that the accident has given him superspeed. Dr. Eobard Thawne, the wheelchair-bound CEO of S.T.A.R. Labs, vows to help Barry and selects a team of scientists, led by Valerie, to test his powers.
>Barry bonds with Valerie and she finds out he's a comic book fan, particularly of the Flash, Jay Garrick. Thawne mentors Barry in how to control his powers and reveals his plans to build a particle accelerator and explore the Multiverse.
>When Barry returns home, he reunites with Iris, and they share a moment before he is reminded she's engaged and she regretfully leaves.
>Barry confirms that the unidentified woman was frozen to death and finds out the responsible is Leonard "Cold" Snart, a serial killer who watched his entire family burn to death in a house fire, and became obsessed with the cold.
>Chyre issues an arrest warrant for Cold, and is later kidnapped by him. Cold executes Chyre on live television and announces he'll destroy a Central City landmark in five days.
>Barry and Iris work together and figure out Cold's target is the Central City Train Station. Barry heads there and evacuates the entire place before a bomb Cold planted is detonated. Iris watches the CCTV footage of the evacuated and catches glimpses of Barry in action. Though she doesn't see his face, she begins writing about the "guardian angel", and Barry becomes concerned his identity will be exposed.
>Barry and the scientists go to a bar to celebrate what Barry has accomplished without Thawne knowing. Iris and Nathan are passing by and spot Barry with Valerie. Iris gets jealous. Barry and Valerie have sex.
>Barry is decided to catch Cold before he makes another victim. Valerie gives him an experimental uniform she made without Thawne's permission, based in Garrick's old suit from the comics. She calls Barry "The Flash".
>Barry figures out that Nathan is Cold's next target and rescues him and Iris just as Cold attacks them. He defeats Cold, who is arrested, and saves Nathan, who is nearly frozen to death. He later leaves a note to the paramedics with instructions on how to proceed with Nathan, and Iris recognizes the handwriting, deducing that Barry is the Flash.
>At the hospital, Nathan confides with Iris that he laundered money for the people that Cold later killed, and their investments were all connected to S.T.A.R. Labs. Iris is disgusted Nathan withheld this information to preserve his reputation and breaks up with him.
>Barry interrogates Cold, who announces "he" is coming. Suddenly, Barry is attacked by a black-clad speedster, Zoom, who tells him to "stop running" and reveals himself as the murdered of Barry's mother.
>Barry confides with Iris that he's scared of what Zoom might do, but Iris encourages him to be strong.
>Meanwhile, Valerie finds out Thawne is planning to use the particle accelerator to steal Barry's speed. Thawne suddenly rises from his chair and snaps Valerie's neck.
>Barry finds out Valerie was murdered and deduces Thawne is responsible. Meanwhile, Zoom plants bombs across Central City and breaks out the inmates of Iron Heights Penitentiary, including Cold.
>Barry defuses the bomb and assists the police in recapturing the criminals. Meanwhile, Cold kidnaps Iris and takes her to S.T.A.R. Labs on Zoom's instruction.
>Barry arrives there and confronts Zoom, who reveals that he comes from a parallel Universe where Barry is the Flash, and defeated him many times. Wanting revenge, Zoom crossed over into another dimension, murdered Barry's parents and tortured him his entire life, while secretly building the particle accelerator with the objective of travelling through the entire Multiverse, finding each version of Barry Allen and torturing them to the breaking point. After he's done, he'll destroy each Universe, so Barry can know how many people he failed.
>Zoom also plans to steal the speed of all versions of Barry after they receive their powers. Once he's powerful enough, he'll undo Barry from creation itself, and reshape History across the Multiverse to his liking.
>Zoom activates the particle accelerator and orders Cold to kill Iris. Cold throws a needle at her, but Barry backhands it into Cold's chest, and he dies feeling "warm".
>Barry fights Zoom and taps into the Speed Force. Once Zoom is defeated, Barry leaves him there, where Zoom is trapped forever.
>Barry destroys the particle accelerator before it destroys the Universe, and is briefly pulled into the threshold of the Multiverse and catches a glimpse of Zoom's home Universe, where his parents are alive, happy and proud of his accomplishments as the Flash.
>Barry is returned to his original Universe and reunites with Iris. Inspired by his legacy and the memory of his parents, he decides to continue fighting crime as The Flash. Barry and Iris develop a romantic relationship.
>In an after-credits scene, Barry runs into Green Lantern Hal Jordan, impressed that Barry can reach the speed of light.
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