Grant Gustin as Barry, Carlos Valdes as Cisco
Cisco (Carlos Valdes) accidentally wipes off Barry’s (Grant Gustin) memory in the trailer for Season 3, episode 21 of “The Flash.” The CW

Barry (Grant Gustin) and his team are taking drastic measures to stop Savitar in Season 3, episode 21 of “The Flash.”

At the end of last night’s Season 3, episode 20, Barry figured out that Savitar is actually a version of himself from the future, which explains why the villainous speedster has always been one step ahead of Team Flash. That, however, may no longer be the case after Cisco (Carlos Valdes), as revealed in the trailer for episode 21, thinks of a way to potentially stop the God of Speed from remembering everything the Scarlet Speedster does.

READ: Why do Caitlin’s unrepressed powers turn her into Killer Frost?

“What if Barry can’t remember what we’re doing now?” Cisco asks the team in the preview clip.

“You will mess with his brain?” Joe (Jesse L. Martin) asks.

“Just a little bit,” Cisco replies, before telling Barry that he wants to stop him from making new memories.

Barry agrees with the plan, but the result isn’t something they expect.

“Who are all you?” asks Barry after Cisco messes with his friend’s brain. “Where the hell am I? Is this a dentist office?”

While the team figures out the right way to make Barry forget, H.R. (Tom Cavanagh) continues to push Tracy Brand (Anne Dudek) to design the trap for Savitar. Meanwhile, Killer Frost (Danielle Panabaker) returns with an interesting proposal.

At the end of episode 19, Killer Frost aligned herself with Savitar, and with the recent revelation that Savitar is actually a version of Barry from the future, Killer Frost’s unexpected alliance with baddie now makes sense.

In a recent interview with Entertainment Weekly, executive producer Andrew Kreisberg explained their decision to make Savitar a version of Barry from the future. “The idea that the darkest villain we could come up with was actually a very damaged version of our hero was interesting and fresh to us,” Kreisberg said. “We’re not only competing with all the stuff that we’ve done on ‘Flash,’ but we’re always competing with everything we’ve done on all the other shows. So to have our lead actor be both the hero and the villain isn’t something we’ve done before, so that was exciting for us as storytellers.”

Kreisberg added that making Savitar a version of Barry from the future created an opportunity for Gustin to show off his acting chops. “What’s so amazing about these last few episodes, especially when you think about it in terms of [episode 19] ‘Once and Future Flash,’ is Grant made the future Flash a very distinct character,” the exec producer said. “He does the same with Savitar, especially in scenes where he has to act with himself. If everything Grant has done up until now, including the musical, hasn’t blown you away with his talent, I think when you see scenes of him and Savitar together, you’re really going to be blown away because he’s found a whole new speed for him.”

Although Savitar’s identity has already been revealed, the show has yet to explain why a future version of Barry would want to kill his fiancée Iris West (Candice Patton). “You get that in the next episode, and the mystery is ongoing, but obviously Savitar is a version of Barry Allen, a heavily scarred version,” Kreisberg said.

“The Flash” Season 3, episode 21, titled “Cause and Effect,” airs on Tuesday, May 9 at 8 p.m. EDT on The CW.