The Flash learns that Captain Cold and Heat Wave have returned to Central City. This time Snart has brought along his baby sister Lisa to help wreak havoc on the city.

Barry, Caitlin, Cisco and Joe set a trap for Wells. Cisco uses himself as prey which puts him in grave danger. Meanwhile, Eddie makes a decision regarding Iris, which leaves Joe a bit unsettled.

Wells presents Barry with a life-changing choice. Dr. Martin Stein and Ronnie Raymond return to help the S.T.A.R. Labs team with this final fight.

Picking up months after the Singularity attacked Central City, Barry is still struggling to forgive himself for Eddie’s death. Concerned about putting his friends in danger, Barry has pushed everyone away and has chosen to protect the city on his own. When a meta-human named Atom Smasher attacks the city, Iris tells Barry that he needs to let his friends help him protect the citizens of Central City. Meanwhile, Cisco helps Joe with his Meta Task Force.

Barry and the team look for another Firestorm match for Dr. Stein. When the team meets Jefferson "Jax" Jackson, Caitlin has her reservations about whether Jax is the right match for Dr. Stein. Iris surprises Joe while Barry and Patty grow closer.

Grodd returns to Central City and kidnaps Caitlin. Barry and team race to find her before it’s too late. Meanwhile, Cisco plans his first date with the new barista at Jitters, Kendra Saunders and Patty begins to suspect Barry is hiding something from her.

Now that they've grown closer, Barry considers telling Patty that he is The Flash. Meanwhile, Joe and Iris try to get to know Wally, and the team hunts down a meta-human who can slow time itself.

Barry, Wells and Cisco journey to Earth-2 to rescue Wells’ daughter, Jesse from Zoom. Barry is stunned when he runs into Earth-2 Iris and Joe, but nothing prepares him for meeting Killer Frost and Deathstorm. Meanwhile, back on Earth-1, Jay has to take over the Flash’s responsibilities when a meta-human nicknamed Geomancer attacks Central City.

Having arrived in town intent on creating maximum chaos, Trajectory's antics are misinterpreted as having been perpetrated by the Flash himself. Barry thus must quickly uncover the mystery of who is the girl under the mask — as well as what is driving her mad desire for speed and destruction.

A meta-human with super strength named Griffin Grey mistakes Harry for Earth-1 Harrison Wells and kidnaps him, demanding that Wells cure him from his current condition. Realizing another brilliant Wells could help track Griffin’s location, Barry asks Jesse to help. Meanwhile, Wally corners Joe about The Flash.

After Zoom unleashes an army of Earth-2 meta-humans on Central City, Barry is shaken when he sees their leader is the Black Canary’s Earth-2 doppelganger, the Black Siren. Meanwhile, Wally takes to the streets to help The Flash stop the meta-humans, which worries Joe. Iris and Henry are concerned about Barry taking on Zoom.