1. Pilot

The episode begins with Barry Allen, a forensic crime scene investigator for the Central City Police Department, recounting his youth, in which his mother was murdered by a yellow blur in a lightning storm, and his father was wrongly imprisoned for the crime. Fourteen years later, in 2013, Barry and his best friend Iris West attend the unveiling of a particle accelerator at S.T.A.R. Labs created by Dr. Harrison Wells. Meanwhile, Iris' father, Detective Joe West, and his partner Fred Chyre use evidence Barry discovered to find Clyde and Mark Mardon. Clyde kills Fred as they escape on a plane. Meanwhile, the particle accelerator explodes, creating a storm cloud and unleashing a wave of dark matter. The Mardon brothers are presumed dead after their plane crashes, and Barry is struck by lightning.

Nine months later, Barry wakes up from a coma in S.T.A.R. Labs and meets Caitlin Snow, Cisco Ramon, and Wells, who needs a wheelchair following the explosion. Barry experiences superhuman speed and the S.T.A.R. Labs team test his abilities. Clyde later resurfaces with the ability to control the weather. Barry unsuccessfully tries to stop him, though he is able to identify him and his superhuman powers to Joe, who refuses to believe him. Barry confronts the team about the other " metahumans " created from the explosion, wanting to stop Clyde, but Wells doesn't want to risk the "treasures" within Barry's genetics. Feeling lost and hurt, Barry pays a visit to Starling City 's Oliver Queen, alias "the Arrow", who encourages him to his heroic potential.

Barry returns to Central City and convinces Caitlin and Cisco to help him stop Clyde and other metahumans. To that end, Cisco gives Barry a suit that will withstand the friction created by his high-speed movements. Tracking Clyde to his old hideout, Joe and his new partner Detective Eddie Thawne, discover both his survival and his newfound powers. Barry arrives and is able to stop Clyde, who is killed by Joe. Learning about Barry's speed, Joe apologizes for not believing him, and asks him to keep this secret from Iris. With his new powers, Barry runs to help people and vows to one day exonerate his father.

In S.T.A.R. Labs, Wells enters a secret room. He rises from his wheelchair, and looks upon a holographic image of a newspaper (published on April 25, 2024) with a headline that reads "Flash Missing, Vanishes in Crisis ".