Season synopsis
Contains spoilers for this season and earlier seasons.
Despero arrives convinced that Barry will cause a future catastrophe. Barry’s life begins unraveling, and he discovers that Thawne has rewritten history: Joe is dead, Barry is the Reverse-Flash, and Thawne has taken his place beside Iris. With Damien Darhk’s help, Barry restores the original timeline. He then defeats Despero and saves Thawne from erasure by removing his speed, choosing imprisonment over letting his enemy die.
A series of incinerations leads the team to a black flame that feeds on grief. Caitlin believes it contains Ronnie and tries to bring her husband back, but the apparent reunion releases Deathstorm. Frost transforms herself to fight him and destroys the threat at the cost of her life. Caitlin cannot accept losing her sister and recruits Mark to help resurrect her. Meanwhile Iris suffers a time sickness that makes people and objects disappear and eventually pulls her into the Still Force.
The Negative Forces reveal that Iris’s illness is part of their retaliation for Barry depowering Thawne. Iris is struck by Barry’s lightning during their confrontation, and Thawne returns as their empowered avatar. Her consciousness survives inside Damien’s Time Stone, allowing her to return and urge Barry to stop escalating the fight. Barry remains still as Thawne demands more power and is destroyed by his own excess. Iris recovers, but Caitlin’s resurrection chamber produces an unexpected person whom Mark does not recognize. A blue crystal in a future laboratory signals that the Negative Speed Force’s threat can return.