When Barry Allen was a boy, his father was falsely convicted of his mother’s bizarre murder. Raised by Detective Joe West, his best friend Iris’s father, he constantly searched for the truth. Now a brilliant CSI Investigator, he is fascinated by physicist Harrison Wells and his S.T.A.R. Labs team’s latest invention. But when it’s tested, an explosion puts Barry into a coma. He awakens with the power of super speed, rendering him virtually unseen. Soon Barry discovers a nefarious group of “meta-humans” also created that night, threatening Central City. Along with clearing his father’s name, Barry has a purpose: to be the city’s guardian angel, known as The Flash.
Barry (Grant Gustin) and team are surprised when Mon-El (guest star Chris Wood) and Hank Henshaw (guest star David Harewood) arrive on their Earth carrying a comatose Supergirl (guest star Melissa Benoist) who was whammied by the Music Meister (guest star Darren Criss).
Desperate to stop Savitar and save his friends, Barry (Grant Gustin) turns to the speed force for answers.
While training with Barry (Grant Gustin), Wally (Keiynan Lonsdale) starts to have visions of Savitar, which he hides from the team.
When Grodd (voiced by David Sobolov) and his army of gorillas bring the battle to Earth-1, The Flash (Grant Gustin) and team must find a way to stop them before they destroy Central City.
When Jesse Quick (guest star Violett Beane) informs the team that her father (Tom Cavanagh) has been abducted, Barry (Grant Gustin), Caitlin (Danielle Panabaker), Cisco (Carlos Valdes) and Julian (Tom Felton) voyage to Earth-2 on a rescue mission to save Harry from Gorilla City.
Barry (Grant Gustin) and the team at S.T.A.R. Labs work together to bring down Clive Yorkin (guest star Matthew Kevin Anderson), a criminal meta-human who is methodically killing people by causing them to decompose at an accelerated rate.
H.R.’s (Tom Cavanagh) past catches up with him when a bounty hunter with vibe powers named Gypsy (guest star Jessica Camacho) arrives in Central City to bring him back to Earth-19 to stand trial for his crime.
Barry (Grant Gustin) is tormented by his vision of the future where Iris (Candice Patton) is murdered by Savitar.
With Alchemy and Savitar still looming threats, Barry (Grant Gustin) is unable to focus on the Christmas holiday, and especially his relationship with Iris (Candice Patton).
When aliens called the Dominators attack Central City, Barry (Grant Gustin) speeds over to Star City to ask the Green Arrow (guest star Stephen Amell) for help in stopping them.