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"Cisco told me – or showed me – that you all haven't been a team in a long time. And I know that I'm the reason for that. Iris' death shouldn't have driven me away from you all. I mean, it should've driven me closer. This isn't what she would want. But I'm here now to tell you that no matter what happens in the past, I will not abandon you."
Barry Allen bringing Team Flash back together in the future

"The Once and Future Flash" is the nineteenth episode of the third season of The Flash, and the sixty-fifth episode overall. It aired on April 25, 2017.



Barry works out that he needs to travel to 2024, since he knows he's still around in that time and Savitar isn't. Iris asks him to promise that he'll be there for Joe if anything happens to her. Barry initially refuses to discuss it but eventually agrees. He then gets an alert of a metahuman at STAR Labs. Caitlin, now in her Killer Frost persona, attacks Cisco, H.R. and Julian. Julian tries to reach the necklace but she freezes it. Cisco manages to blast Caitlin and they take refuge in the pipeline, only for her to reveal she still has access to it. The Flash arrives and Killer Frost ends up freezing the doorway, escaping in the time it takes him to get through it.

Cisco and Julian argue over their handling of Caitlin, until Barry calls time out. Barry then tells Iris, Joe and Wally that he's going to time travel to the future immediately. He has Kid Flash give him a boost to open a portal to the future and emerges in a desolate 2024. He is immediately confronted by first Top, who gives him vertigo, and then Mirror Master, who declares it is now their town and gives him a beating until he speeds away.

Barry visits his old apartment, now wrecked and neglected. Cisco arrives, having seen him on CCTV, and quickly deduces he's there because of Savitar. He takes him to what's left of STAR Labs: H.R. moved on, Caitlin never returned after becoming Killer Frost and Barry closed the museum. Barry finds his future self, who tells him he can't save Iris and admits he doesn't know who Savitar is. He tells Barry to go back and make memories with Iris while he can.

To Cisco's disappointment, Barry decides to go back. Cisco reveals Killer Frost destroyed his arms, robbing him of his powers, and he has mechanical replacements. The Flash tries to open another portal but fails and wonders if Mirror Master and Top did something to him. Cisco reassures him with the fact that he can always return to the time he left. He takes Barry to the lab where Julian now works, with Caitlin, still in her Killer Frost persona, caged up. Caitlin immediately realises he's from the past, since he doesn't hate her yet. She reveals she teamed up with Savitar, who taught her to embrace being Killer Frost. Barry realises she knows who Savitar is. Caitlin says she'll never tell but reveals Wally also encountered Savitar.

Barry and Cisco go to the West house and are met by a nurse, Beth, who knows Cisco but only recognises Barry from photographs. They find Wally catatonic in a wheelchair. Cisco reveals he went after Savitar when Iris was killed; Joe found him the next day with his spine broken and he's been in shock ever since. Cisco deduces Joe must be at Iris' grave. Barry goes to find him. Without looking at him, Joe says he left him when Iris died. Barry tracks down his future self in the Time Vault and blasts him for breaking his promise to Iris. Future Barry replies that he was broken when Iris died, despite him creating time remnants to fight Savitar, even after he finally trapped Savitar in the Speed Force.

Barry tells Cisco there's nothing he can do and wants to go back. He realises Cisco wants him to stay and was the one who stopped him leaving. Cisco has set up a device to stop him gaining enough momentum to open up a portal and tells him to go if he wants. He nearly does but accepts he can't leave the future like this. H.R. is in Jitters, which he apparently now owns, giving a reading of a bodice-ripper he wrote under the name H.R. Wells to a crowd of appreciative women who send him flirtatious texts. Barry grabs him and super-speeds him to STAR Labs, along with Julian and Joe. Joe finally realises Barry is from the past. Barry apologises for abandoning them and says Iris' death should have brought them together. Cisco gets an alert of a raid by Mirror Master and Top, and Barry asks the others to reunite as Team Flash to help stop them. They agree.

Scudder and Dillon have just robbed a jeweller's when the Flash arrives, on coms to STAR Labs where Cisco, Joe, H.R. and Julian are restoring the old mission control. Top quickly causes vertigo and Mirror Master starts to topple a glass building towards him, threatening to force him into a mirror on the floor. Cisco reprogrammes his device to protect them from the pair's powers but has no way to get it to Barry. Future Barry appears, having been monitoring them from the Time Vault, and says he'll do it. Donning his old suit, the Future Flash speeds his younger self out of danger and then activates the device. Scudder and Dillon try to flee separately but Past Flash ties Top up, while Future Flash follows Scudder into a mirror and pulls him out of it.

Later, the reformed Team Flash observe a newsreader, Kline, appreciatively reporting how two Flashes caught the villains. Future Barry agrees they should work together to clean up the city. H.R. leads the others to free coffee at Jitters. Future Barry gives his past self one piece of information: The Speed Trap he used to trap Savitar was constructed by Tracy Brand, but she won't develop the technology until four years ago. He gives Barry a copy of her research in the hope she can decode it.

After saying goodbye to Cisco, the Flash returns to the point where he left. He tells the remaining Team Flash what he learned, including the fact that Caitlin will join up with Savitar, meaning they have to find her before that happens. He also promises Joe he'll always be there for him.

Killer Frost is confronted by Savitar in the woods. He tells her he's been waiting for her and wants to stop her ever becoming Caitlin again. Killer Frost asks why she should trust them. Savitar emerges from his suit, revealing his face to her. Killer Frost immediately asks what he needs her to do.



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  • This episode aired on April 25 and takes place in 2024, the date on which the Flash is said to vanish in a Crisis, as published in a newspaper in the Time Vault.
    • However, the date Barry arrives in the future is February 3, 2024.
      • DC has officially called the day Flash Time Travel Day.
  • The title is a nod to an infamous inscription purported to be on the tomb of the legendary King Arthur in Le Morte d'Arthur by Sir Thomas Malory.
  • The title of this episode is a reference to the 1958 novel The Once and Future King by T.H. White, as well as the comic book The Flash #79, which was entitled "The Once and Future Flash".
  • While hiding in the Pipeline, H.R. slides under the closing door and retrieves his drumstick in the same manner that Indiana Jones does for his hat in Indiana Jones and the Temple of Doom.
  • While hiding from Killer Frost, H.R. and Cisco sing "Swing Low, Sweet Chariot", an African-American spiritual popularized by Eric Clapton.
  • In the future of this timeline, Barry and his friends' fates are revealed:
    • In the battle that Cisco vibed between him and Killer Frost earlier in the season,[1] she managed to freeze and shatter his hands, effectively depriving Cisco of his powers. Later, Cisco replaced his hands with mechanical prosthetics.
    • Killer Frost is arrested and incarcerated at Iron Heights Prison, with Julian taking care of her.
    • Wally went after Savitar by himself after Iris' death. Unfortunately, he lost and his spine was shattered, rendering him paraplegic. The aftermath of the fight sent him into a great shock for 7 years.
    • Joe doesn't get over Iris' death and regularly visits her grave.
    • H.R. is a celebrated author, having written a book titled The Streak vs Mr. Reflecto and reinvented CC Jitters into "HR Jitters".
    • Barry stopped being The Flash sometime after he defeated Savitar. He shut down S.T.A.R. Labs and began living there, abandoning his friends and leaving them without support.
  • This episode shares many similarities with the DC's Legends of Tomorrow episode "Star City 2046"​:
    • Both episodes take place in the future and feature an older broken hero (Barry in The Flash and Oliver Queen in DC's Legends of Tomorrow) living as a recluse in the remnants of their old hideout.
    • In the heroes' absence, a group of villains control their respective cities.
    • The heroes return to action when their former teammates inspire them and make them realize that their respective cities will always need them.
    • The episodes end with the heroes reforming their team and cleaning up their old hideout.
    • In both of these potential futures, someone has lost a limb and uses prosthetics to compensate; In 2046 Star City, Oliver is missing one of his arms (cut off by Grant Wilson) and uses a mechanical arm. In 2024 Central City, Cisco has lost both of his hands (shattered by Killer Frost) and uses a pair of mechanical hands.
  • This episode marks Tom Cavanagh's directorial debut.
  • This episode marks the first appearance of The Flash's new suit, which Barry wears the following season.
  • This was the first episode to feature Killer Frost but not Caitlin Snow in any capacity.
  • When he is face-to-face with Killer Frost, Julian has a lighting-bolt scar on his forehead, much like Harry Potter. Tom Felton portrayed Draco Malfoy in the Harry Potter film series.
  • Iris is mentioned to be born on June 24, 1989. This is exactly one year after Candice Patton's real-life date of birth.


  • Iris' birth date is shown on her tombstone to be June 24, 1989. However, Eddie Thawne stated that her birthday was "two months from now" in the portion of "Flash Back" that took place during the time period of "The Sound and the Fury", which aired in late January and presumably took place around the same time in-universe. This would place Iris' birthday sometime in March or April.
  • In 2024, H.R.'s face is pictured on his book and its promotional material, despite the general public knowing "Harrison Wells" to be the man who murdered Nora Allen.
  • When Barry was in 2024, he referred to himself as being from 2017. However, when he got home and H.R. asked him which year he went to, Barry said that he traveled eight years into the future instead of six (Barry time travelled from March 28th 2017 to February 3rd 2024 which is six years from 2017 and it would be seven years if the date on the newspaper article would be full eight years if the newspaper article wrote February 3rd 2025.
  • When future Barry told Barry from 2017 that Tracy Brand figured out the technology on how to trap Savitar in the Speed Force four years ago. At this point of time, which would be 2024, this would mean if Barry was rounding the time to four years, either the year 2019 or 2020 was when Tracy invented the Speed Force bazooka in Future Barry's timeline. The Barry from 2017 said "four years after Iris died". In actuality, it would be around two to three years after Iris died.