The Flash season 3, episode 21 synopsis: “Cause and Effect”


This week on The Flash, Barry wipes his memories as a strategy to defeat Savitar.

Last week on The Flash‘s “I know Who You Are” episode, the team was on a mission to find the only person with the know-how to trap Savitar in the Speed Force. Their task was made even more difficult when Savitar sent Killer Frost to find the same person.

Tracy Brand was the goal for Team Flash. When Barry traveled to 2024, his future self told him that the Nobel Prize-winning scientist would develop a method to trap Savitar in the Speed Force—however, it would be four years too late. At that time, Iris would’ve already been killed.

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The team tried to fast-forward Brand’s science by first finding her and divulging theories that haven’t even been discovered. When they do find Brand, they learn that she’s a disillusioned graduate student who had been laughed out of her dissertation defense. Team Flash had to use their powers of inspirational persuasion (and some H.R. charm), but she eventually came around.

With Brand now under the protection of the team, Killer Frost uses another method to get to her—by kidnapping Cecile and offering a trade. Team Flash agrees, but in reality, sets a trap for Killer Frost. It works, and they’re able to save Cecile and keep Brand safe.

As the team briefly celebrated their small victory, Barry received an epiphany. Traveling to a remote street location, he called out Savitar. There, Barry confronted the God of Speed, revealing that he had deduced his true identity. Savitar, emerging from his armor, confirmed that he is, in actuality, a future version of Barry.

This week, Barry goes to great lengths to make sure that the future version of himself will have no knowledge of the past. Thus, taking away a key advantage from Savitar. Here’s the official synopsis from The CW:

“Cause and Effect”

"Barry (Grant Gustin) takes drastic measures to stop Savitar. Meanwhile, H.R. (Tom Cavanagh) continues to push Tracy Brand (guest star Anne Dudek) to design the trap for Savitar and Killer Frost (Danielle Panabaker) returns with an interesting proposal."

And here’s the exciting promo:

Next: Catch up with a recap of 'I Know Who You Are'

Enjoy this week’s episode, and check back with us on Wednesday morning for our full recap and review. Also, on, our friends will be doing The Flash Recaps. The excitement continues on Fridays as also gives fans a weekly round-up of The CW’s superhero universe—Supergirl, The Flash, Arrow, and DC’s Legends of Tomorrow—with their DC TV Universe special.

The Flash airs on The CW on Tuesdays at 8:00 p.m. EST.