When a powerful alien threat arrives on Earth under mysterious circumstances, Barry, Iris and the rest of the team are pushed to their limits in a desperate battle to save the world.
Despero warns The Flash that great tragedies will lead to Armageddon; Barry doubles down on proving his innocence, but a devastating revelation pushes him to seek counsel from Black Lightning.
Barry meets Black Lightning at the Hall of Justice after things take a dire turn with Despero; Iris suspects something is off with Despero's vision of the future so she seeks help from a powerful ally.
Barry is shocked when Eobard Thawne returns in the most unexpected way, and with a tie to a loved one. Damien Darhk offers advice to Barry but there is a catch. An epic battle begins with The Reverse-Flash against The Flash and Team Flash.
When a criminal invades the CCPD, Barry and Kramer must trust and rely on each other if they are going to make it out safely; Caitlin learns a valuable lesson while out with Snow and Mark.
Barry trusts his instincts during a murder investigation, believing the suspect, despite the overwhelming evidence against him; Iris gives Allegra an opportunity to be a mentor.
Barry and Team Flash get closer to figuring out the Fire Meta but no closer to finding him; Iris, needing a distraction, follows a story to Coast City.
Barry's desire to keep the team safe is tested when Frost recklessly courts danger while trying to stop the Black Flame; Iris tries to help a teen girl reunite with her mother but unintentionally does more harm than good.
Barry and Chester may have found a way to stop the Black Flame from hurting anyone else; Caitlin decides to handle a situation on her own, possibly putting more innocent lives in danger.
With a new Meta terrorizing the city, Joe lends a hand to the local authorities; Barry gets an assist from Cecile who helps to track the mass murderer.
A new speedster in town gives The Flash more than he bargained for; Cecile's powers experience a growth spurt, allowing her to aid Team Flash on an entirely different level.