“Cause and Effect” is episode twenty-one of season three of The Flash.
In the previous episode, “I Know Who You Are”, Barry figured out who Savitar was, and it was indeed someone known to them. It was Barry Allen inside the suit, albeit a scarred one. Savitar has said to Barry what sounded like ‘I am the future, Flash’ but what he actually said was ‘I am the future Flash.’ What a difference a comma makes. Savitar claimed he created himself, which he probably did by killing Iris and setting events in motion.
The episode opens immediately after the last. Savitar states that he outgrew red and Barry says he is a time remnant, a temporal duplicate. Savitar mentions Barry doing that in “The Race of His Life” in order to stop Zoom, and that remnant died saving the multiverse. Barry went happily along with his life and things would have stayed that way. If not for “Flashpoint”. Which changed everything. Future Flash, when Barry travelled forward in “The Once and Future Flash”, created time remnants to fight Savitar, and Savitar slaughtered them. All but one of them, according to Savitar Barry – himself. He lived, but Barry, Joe, Wally and Cisco shunned him as an aberration, not the true Barry Allen.
Savitar Barry was broken. He realised a god feels no pain, so decided to become one. It needs two things. The first is for Iris to die so that Barry is driven far enough to the dark that Savitar is born. The other thing Savitar will keep to himself. Barry suggests killing himself, as Eddie Thawne did in “Fast Enough” in order to stop Eobard Thawne. Savitar says that didn’t work out so well for Eddie, because Thawne is still around (well… maybe not). The more you do time travel, the less the rules apply to you. Barry attacks Savitar Barry, but Savitar’s suit attacks even without Savitar Barry inside it. Both cast lightning at each other and, after the explosion, Savitar is gone.
Barry heads back to S.T.A.R. Labs and fills the others in. Savitar isn’t Barry; he’s the worst parts of Barry. Which Cisco compares to the transporter malfunction in the Star Trek: TOS episode “The Enemy Within” which created an Evil Kirk. Julian says that’s why Caitlin was willing to follow Savitar; he has a face she trusts. Half of one, according to Barry. Cisco realises that the message the Legends found on the Waverider in “Shogun” about not trusting Barry Allen was referring to Savitar. Well, probably.
Cisco then explains that four years in the future Barry creates time remnants to fight Savitar, and Savitar lets one live to become Savitar. That remnant travels back through time to become the first speedster and build up a cult. Joe can’t make sense of this. Cisco tells him it’s a closed loop. They also realise that Savitar is based on a future version of Barry, so remembers everything that Barry and the others did to stop Savitar. Inconvenient.
Barry talks to Iris about how he understands how a speedster could become a god and how Savitar comes from the pain and loss inside him. Then Cisco says he has had the best idea ever. Or the worst. He and Julian have come up with a way of stopping Barry making new memories. Savitar can stop them, because he remembers doing it, so if he can’t remember what they did to stop Savitar – by messing with Barry’s brain a little – they could stop Savitar from being two steps ahead. Joe thought Caitlin was the expert on brains. Yes, she was. There’s no way this can go wrong.
So, Barry’s brain is messed with. He says he feels fine. Only who is Barry? And who are they? A slight miscalculation according to Cisco. Joe would not use the word ‘slight.’ When Barry is told he is in a lab he asks if they were experimenting on him. Julian tells him no… then says, well, yes, they were. But it is consensual. Barry checks his driving license and decides he wants to be called Bart not Barry. He’s also freaking out a bit.
There’s no sign of structural damage to Barry’s brain. Julian believes he’s suffering from amnesia and perhaps they didn’t account for the neural velocity caused by Barry’s superspeed. Barry no longer knows he has superspeed. Then Cecille contacts Joe; she needs Barry urgently at CCPD. Oops.
H.R. is checking up on Tracy, to see if she can speed up work on the speed trap. It isn’t working and she talks science at him. H.R. tells her to stop talking science, take a step back and think of something that calms her. Coffee calms Tracy. Neither has met anyone else who chills out with copious amounts of caffeine. There’s nearly a moment.
Cecille needs Barry to testify in court against Lucius Coolidge – Heat Monger – the worst arsonist the city has seen since Mick Rory went off the grid. The Flash stopped him and Barry was the CSI. Cecille is told that Barry cannot do that. Cecille, when told why, asked if Barry lost his memories through the evil powers of a supervillain. No, they did it themselves. Accidentally. Why? It’s complicated. This is a problem.
Killer Frost is with Savitar wanting to know why he isn’t doing anything other than kneel on the floor. Savitar grabs her by the throat. And asks who she is. And who he is. Well, some bits of the plan are working.
Bart is overall a far cheerier person than Barry normally is and there are more elements of comedy than might be expected, caused by Barry’s loss of memory. Such as when Wally tells Bart he’s his brother, and Bart checks his skin colour. Then more problems start to arise from Barry’s memory loss.