Flash Season 3 Episode 21 recap: What is a closed loop and how does Savitar exist?

Spoilers for Flash Season 3, Episode 21.

Last time:

Barry found Tracy Brand, and she agreed to help build the speed force trap. Barry realised who Savitar was and confronted him.

Onto the recap:

Savitar explains who he is:

Savitar tells Barry that he is a time remnant that survived the fight against Savitar. When he returned to Team Flash, they rejected him because he wasn’t the true Barry Allen. Broken and alone, he decided to become a God to end the pain.


Savitar says that he needs two things to become a god: Iris to die, and something else that he won’t reveal. Barry threatens to kill himself. Savitar says that it didn’t work for Eddie: Thawne is still around, and the more you time travel, the less the rules apply.

Barry attacks Savitar and tries to break his neck. The Savitar suit moves independently and attacks Barry. Savitar speeds into his suit and he and Barry throw lightning at each other. There is a massive explosion, and Savitar vanishes.

Back at Star labs:

Barry tells the team who Savitar is. Cisco explains that 4 years from now, Barry creates a time remnant to fight Savitar. Savitar lets that remnant live so that it can become Savitar. Joe asks which came first. Cisco says that it is a closed loop with no beginning or end.

Wally asks how they can stop Savitar if Savitar knows everything that Barry does.

Iris talks to Barry:

Barry tells Iris that he recognised the pain in Savitar’s eyes: he sees it in himself when he thinks about his parents. He admits that sometimes, he wants to make someone else hurt as much as he does. Iris tells him that he won’t because he’s a good person, and they will stop Savitar.

Cisco has a plan:

Cisco arrives and says that he wants to stop Barry from making new memories, so that Savitar can’t remember any plans that they make to beat him. Barry agrees. It goes wrong. After Cisco activates the device, Barry doesn’t remember anything, not even his own name.

Barry freaks out:

Barry accuses his friends of experimenting on him. Cisco tries to get him back into the chair to fix him, but Barry refuses. Iris shows Barry some photos of them together, and she convinces him that they are his friends. She tells Barry that they are engaged, and he can trust them.

Cisco tests Barry’s reflexes:

Cisco throws a pen at Barry to see if he knows that he’s the Flash. Barry fails to catch it, so that’s a no. Cecile calls Joe and says that she needs Barry urgently at CCPD. Iris says that her and Joe will take Barry to CCPD, whilst Cisco and Julian figure out how to reverse this.

Tracy and H.R have a moment:

Tracy throws a gear across the floor in a huff. H.R arrives, and Tracy explains that she is stuck. H.R tells her to take a step back. They bond over a love of coffee. As they move towards each other to kiss, H.R panics and leaves Tracy to it.


Cecile explains that she needs Barry to testify in court to hold an arsonist, Heatmonger, for trial. Joe tells her that Barry can’t, he has amnesia. Cecile says that if Barry can’t testify, the bad guy walks. She tells them to figure something out and leaves. Joe follows, leaving Barry with Iris.

Barry questions Iris:

Barry apologises to Iris: Everyone seems upset with him. Iris says that they aren’t upset, they just want him back to normal. Barry asks what normal is: Have they started planning a wedding? Iris says that they’ve been too busy. Barry is baffled: What could be more important than their wedding? Iris tells him not to worry about it, and she takes him to get food.

Savitar loses his memory:

Killer Frost approaches Savitar, who is crouched on the floor. She asks what Savitar’s next move is, because if they don’t act soon neither of them will get what they want. Savitar grabs her by the neck and asks her who she is, and then he asks who he is.

Barry and Iris get coffee:

s03e21 Barry and Iris get coffee.jpg

Iris shows Barry his past: In school, he was a nerd. Barry jokes with her without a care in the world, and Iris is enamoured with him. He gets a text and has to rush off to the court house.

At court:

Cisco gives Barry glasses to wear and tells him not to get them wet. Text appears on the glasses as Julian types what Barry should say. Barry gets nervous, and a drop of sweat breaks the glasses. He can’t manage without Julian, and Heatmonger is released.

Killer Frost visits Star labs:

Wally, Cisco and Julian find Killer Frost waiting in the cortex. Wally tries to run at her, but he doesn’t have his speed because of Barry’s memory loss. Frost says that if they want to fix this, they have to do what she says.

Barry gets his speed:

Iris takes Barry home. He blames himself for Heatmonger going free. Iris smiles and says that is exactly what he would have said before. Barry asks about his parents, and Iris tells him that they died unexpectedly, but peacefully. She lies about how they met too. Barry leans in for a kiss. His hand starts vibrating, and he speeds around the room, out of control.

Killer Frost explains her plan:

Iris takes Barry to Star labs. In the cortex, they see Killer Frost, and Wally explains that he’s lost his powers. Iris tells Barry to give them a minute. Frost explains that Savitar lost his memories too, so he never gave Wally his powers. She says that if they give Barry his memories back, Savitar’s will return too and everything will go back to how it was. 

H.R inspires Tracy:

H.R returns to try and inspire Tracy, but he is distracted and kisses her. It works as inspiration, and she figures out how to finish the trap, now called the speed force bazooka.

Killer Frost works with Cisco and Julian:

s03e21_Killer Frost works with Julian and Cisco

As they work on a device to restore Barry’s memories, Cisco tries to remind Frost of who she is by talking about Ronnie, and saying that all his best memories are with Caitlin. Frost insists that they hurry up: She doesn’t want to be here longer than she has to.

Barry tests his speed:

In the speed lab, Barry is excited about his speed and thinks that he could be a super hero. As he runs around excited, Joe realises that Iris doesn’t want Barry to get his memories back. Joe says that Barry’s memories define him: Without them, their Barry is gone. Iris thinks that the memory loss is a gift: Barry is now unburdened by his dark past.

Barry goes to stop Heatmonger:

Joe tells Barry that he is a superhero, The Flash. Cisco arrives, and he tells them that Heatmonger has set fire to a building. Barry insists that he will stop him.

Barry remembers:

At the burning building, Barry can’t control his powers. Frost says that they need to use her device to restore his memories. Cisco activates it, but Barry still doesn’t remember.

s03e21_Barry and Wally stop Heatmonger

Frost explains that Barry needs a memory to spark his brain. Iris tells Barry that his mum was murdered, and that she comforted him the first night he came to live with them. Her story sparks Barry’s memories, and he and Wally stop the fire. Savitar remembers everything too.

At Star labs:

Joe says that now they can focus on Savitar. Frost sarcastically tells them good luck and heads for the exit. Barry, Cisco and Julian follow, and Julian says that he loves her. Frost says that she doesn’t love him, or any of them, but in the lift, her eyes briefly go brown.

Barry explains that his memories define him:

Barry tells Iris that Caitlin may be too far gone. Iris says that they will get her back, just like they got Barry back. Barry asks Iris if she is sure that this is the him she wants. Iris admits that it was nice to see him without bad memories to hold him back. Barry says that pain and darkness push him to be a better hero, and he wouldn’t change that. Iris kisses him. H.R interrupts.

Speed force bazooka:

H.R and Tracy show the team the finished speed force bazooka. The only issue is they need a power source that has more energy than the sun. They can use one of the Dominator crystals from Invasion, if they can get past King Shark at ARGUS.

How does Savitar exist: What is a closed causal loop?

There are two types of causal loop: closed and open. Cisco was explaining a closed loop with his marker pens. (best explained here) But how can remnant!Barry become Savitar if the reason he becomes Savitar is that Savitar kills Iris and drives Barry to create him?

Before Flashpoint, Savitar didn’t exist to kill Iris: In 2024, Iris West-Allen originally wrote the future article. After Flashpoint, she didn’t. Therefore I think that Barry created Savitar, and the closed loop, when he created Flashpoint. His selfish actions created his worst enemy. Is Savitar a punishment from the speed force for Barry’s constant meddling in the time line?

Honestly, I don’t know. Time travel hurts my head. I hope that next season there’s not so much of it. Perhaps without a speedster enemy, season 4 will be easier to follow!


  • Savitar’s lightning is yellow when he’s outside the suit and white when he’s in the suit. Did Killer Frost power his suit? Is that why he needs her?

  • I love that Barry has to testify in court as a CSI. We don’t get to see CSI Barry as much as we used to, and that’s a shame.

  • Personally, I’m more excited for Captain Cold’s return!


Next time:

Barry recruits Captain Cold to help him steal a power source for the speed force bazooka.

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