Orphaned by tragedy and raised by his best friend's father, brilliant CSI Barry Allen gains powers when lightning strikes him during a freak storm; when another meta-human attacks the city, Barry puts his powers to the test.
Barry experiences a setback while pursuing robbers; Joe is upset with Barry for taking the law into his own hands; Iris becomes more intrigued by the "red streak."
Barry and the team track The Mist -- a dangerous new meta-human with toxic gas powers; Joe decides to visit Henry in jail; Eddie and Iris continue to conceal their relationship.
A villain named Leonard Snart (Wentworth Miller) gets his hands on a "cold" gun -- which could kill Barry; Joe gives Iris the silent treatment.
Gen. Eiling (Clancy Brown) and the Army take over the case after a bomb goes off downtown, drawing Joe's suspicion; after refusing to stop writing about "the streak," Iris receives a visit from the Flash.
A new meta-human is able to turn himself into girded steel; Cisco has a plan to take Tony down; Iris gets in trouble over her blog on Flash; Joe seeks Dr. Wells help in solving Nora Allen's murder.
The Flash goes up against Blackout, a metahuman who can harness electricity; Tockman takes several people inside the police department hostage.
Barry is thrilled when a case brings Oliver, Diggle and Felicity to Central City; a metahuman named Ray Bivolo -- who causes people to lose control of their emotions -- infects Barry; Eddie wants a task force to stop the Flash, infuriating Iris.
Barry enjoys holiday traditions with Joe and Iris -- and is faced with his nemesis; a touching moment with Iris is interrupted by Eddie's arrival.
Leonard Snart returns to Central City with a new partner, a plan to steal a multi-million dollar painting -- and to abduct someone close to Barry; Iris deals with Barry's confession.
Dr. Wells' former protegee -- who can manipulate sound waves -- returns to seek revenge; Iris starts a new job; Joe asks Eddie for a favor -- and asks him to keep it a secret.
Caitlin takes Barry out to a karaoke bar, hoping they both meet someone new; Cisco thinks about Hartley's dangerous proposition; Henry's snooping gets him into trouble.
Barry and the team realize they must pursue Ronnie after he attacks a physicist; Barry struggles to balance his new relationship and his responsibilities as the Flash; Joe asks Cisco for help investigating Nora Allen's murder.
Caitlin is thrilled to have her fiance back after an explosion separates Ronnie and Dr. Stein; Mason Bridge tells Iris that something mysterious is going on at S.T.A.R. labs; Barry receives important information about time travel.
Mark Mardon, also known as the Weather Wizard, targets Joe, who shot Mark's brother, Clyde; Cisco starts to wonder if Joe was right about Dr. Wells; Linda, Barry, Eddie and Iris wind up on an awkward double date.
Leonard Snart returns -- this time with his younger sister as well as Heat Wave -- to wreak havoc on the city.
A villain mimics a criminal mastermind known as The Trickster (Mark Hamill) -- who has been imprisoned for 20 years; Henry is abducted; Iris turns to Eddie for help with a case; flashbacks reveal how Dr. Wells developed the particle accelerator.
Felicity Smoak and Ray Palmer come to Starling City seeking help with Ray's suit; a metahuman named Brie Larvin (Emily Kinney) releases deadly robotic bees; a group dinner does not go as planned.
Joe and Cisco go to Starling City where they ask Capt. Lance for help with their investigation into Dr. Wells; the Black Canary asks Cisco for a favor; Barry is faced with a foe who can transform himself into anyone he touches.
Cisco uses himself as prey in a trap he sets up for Wells with Barry, Caitlin and Joe; Eddie's decision about Iris leaves Joe unsettled.
Barry deals with the latest threat from the Reverse Flash; Dr. Wells distracts the team by releasing Grodd on the city; Iris and Barry have a serious talk.
Barry reaches out to Capt. Cold (Wentworth Miller) for help as Wells gains the upper hand, even though Joe and Caitlin think Cold can't be trusted; Arrow (Stephen Amell) and Firestorm (Robbie Amell) arrive to assist Barry.