When Mark Mardon AKA The Weather Wizard returns to break Leonard Snart AKA Captain Cold and James Jesse AKA The Trickster out of Iron Heights, Barry must stop these rogues from taking over Central City during Christmas. Meanwhile, Joe and Iris meet Wally West.

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.

When Cisco gets a vibe of Eobard Thawne, Barry and the team don’t believe it. But, after an attack at Mercury Labs, Christina McGee confirms that the Reverse Flash is back. Meanwhile, Iris and Francine share a nice moment that brings Iris closer to her brother, Wally.

Barry teams up with Wells to figure out a way to close the breaches, but they are distracted by a meta-human nicknamed Tar Pit who can transform into liquid asphalt. Iris is concerned for Wally’s safety after she finds out about his drag racing hobby. When he refuses to stop she makes a bold move that puts her in danger.

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.

When King Shark escapes from an A.R.G.U.S. holding tank, Lyla and Diggle travel to Central City to warn The Flash. King Shark shows up at the West house and attacks Joe, Iris, Wally and Barry.

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.

After the shocking revelation that Zoom is Jay Garrick, Barry is more determined than ever to get back to Earth-2 to stop Zoom forever. Desperate to find a way to increase his speed, Barry decides to travel back in time and masquerade as his earlier self in order to get his arch-nemesis, Dr. Harrison Wells/Eobard Thawne, to teach him how to run faster. However, things don’t go as planned and Barry is stunned to face familiar foe Hartley Rathaway, as well as old friend Eddie Thawne. Iris makes peace with her past in order to embrace her future.

Equipped with the tachyon device, Barry believes he is fast enough to stop Zoom and wants to open the breaches to catch him. Harry strongly advises against that plan but after Barry convinces him, Harry reveals that Cisco has the power to re-open the breach. Meanwhile, Hunter Zoloman’s painful story on Earth-2 is revealed.

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.

Zoom arrives back on Earth-1 intent on taking over Central City. Barry and Wells come up with a plan to stop Zoom once and for all but it’s extremely dangerous. Unsure if he should take the risk, Barry reaches out to both fathers for advice. Henry is adamantly opposed to Barry risking his life again but Joe thinks he can handle it which puts the two men at odds with each other. Meanwhile, Cisco is shocked when he vibes the Earth-2 villain Rupture, who happens to be his brother Dante’s doppelganger. Rupture came to this Earth seeking justice for Reverb’s death. Iris decides she’s finally ready to open up to Barry about her feelings for him.

With Barry gone, the team must figure out a way to handle the return of an old enemy - Girder. Realizing Girder is retracing his steps from his last attack, Iris volunteers to act as bait to trap him in S.T.A.R. Labs. Meanwhile, Barry fights to return to his old life.

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.

After Zoom reveals his true plan, Barry vows to do whatever it takes to stop him.