- "Barry isn't going to Hell. But like all runners must eventually, he's reached his finish line. His race is over."
- —Speed Force to Team Flash
- Grant Gustin as Barry Allen/The Flash/Savitar
- Candice Patton as Iris West
- Danielle Panabaker as Caitlin Snow/Killer Frost
- Carlos Valdes as Cisco Ramon/Vibe
- Keiynan Lonsdale as Wally Wes/Kid Flash
- Tom Cavanagh as H.R. Wells and Dr. Harry Wells
- Jesse L. Martin as Detective Joe West
Special appearance by
- Jessica Camacho as Gypsy
- Anne Dudek as Tracy Brand
- Michelle Harrison as Nora Allen
- John Wesley Shipp as Jay Garrick/The Flash
- Andre Tricoteux as Savitar
Barry, Joe and Tracy are devastated over Iris' death. But when H.R. drumsticks fall from Iris' corpse, she gasps, and takes away the disguise: Savitar stabbed H.R. Iris wears H.R.'s look, and reveals herself to be alive. It is revealed, that H.R. went after Savitar after he abducted Iris from Earth-2. He found his lair, and managed to free Iris. But they got caught by Killer Frost, and they changed places, without Frost or Savitar realizing the shift. H.R. asks Barry to tell Cisco about something, just before he dies, leaving Tracy devastated. However, Savitar fled with the Speed Force Bazooka. In the forest, Killer Frost is about to kill Cisco, when Savitar arrives, and tells her they need Cisco to build something for them. He then has new memories, and sees that Iris is still alive, with H.R. having taken her place.
In the Time Vault, Barry, Iris and Joe look upon the future article, and it is once again written by Iris, meaning the future has been restored. However, the team agree they still need to stop Savitar, despite the fact, that paradox that erases him, will caught up to him within few hours, as Iris' death was the only thing that keeps him able to exist. In Savitar's lair, Savitar forces Cisco to adjust the Bazooka, so that he can split himself to exist in every possible moment in time. Cisco refuses, but Savitar tells him, if he doesn't, he will kill Caitlin. Not willing to let Caitlin die, Cisco begins working.
Barry comes up with an idea to stop Savitar by doing something he won't expect. He goes to meet him and offers his help to make sure, he keeps on living. They arrive at S.T.A.R. Labs, and Savitar gets an uneasy reception. Although it seems he is willing to accept help, they need Tracy for it. But she refuses to help the man who murdered H.R. Iris has Harrison Wells to be brought to Earth-1 to convince her. He seems to be able to do it. Savitar memorizes amny things, even some that haven't happened yet, but concludes, that when he exists alongside Barry, Iris will still be with him, which leaves him alone. Iris is seemingly able to convince him to bring Cisco and Caitlin back, but when he speeds out, it turns out he set the Philosopher's Stone to self-destruct in the breach lab. Barry and Wally speed everyone out, before the blast destroys the Labs.
In Savitar's hideout, Cisco has finished his work on the Bazooka. He tries to convince Killer Frost, that after Savitar is done with her, he will kill her. Savitar returns and after learning Cisco is ready, he orders Frost to kill him. But with a timely arrival by Gypsy, Cisco is saved. However, he is not particularly happy about it, but Gypsy reveals she knew he was in trouble, because they share a connection. They landed on Barry's apartment, where others are already, and Cisco reveals, what Savitar is trying to do. The team bands together to stop him once and for all.
At the park, where his monument was erected, Savitar and Killer Frost are preparing for his ascension. He opens a breach to the Speed Force, and reveals the reason, why he needed Killer Frost's help. Soon, Black Flash appears from the Speed Force, and Frost freezes him solid and shatters him, as only Frost's ability to freeze things to sub-zero, would be enough to destroy him. Savitar then has Frost use the Bazooka on him. However, the Bazooka doesn't work, and suddenly, Jay Garrick blasts his way out from the Speed Force. Team Flash arrives, and Cisco reveals he sabotaged the bazooka. Enraged, Savitar prepares to fight, taking on Barry, Wally and Jay, while Cisco and Gypsy take on Killer Frost. They are able to defeat her, and she attempts to goad Cisco into killing her. Cisco refuses, and gives her a choice: to use the cure Julian made for her and be rid of her powers. Savitar knocks Barry and CIsco down, and is about to finish Cisco off, when he is struck by a cryokinetic blast, revealing, that Caitlin has resurfaced. Savitar, knowing his end is imminent, is going to kill all of Barry's loved ones before he is erased. But as he is preparing to leave, Barry phases into his suit, and knocks Savitar out from it. He then uses the suit to beat him to the ground, and destroys it afterwards. Savitar urges Barry to kill him, but he won't, not letting his darkness determine, who he is. Victorious, Barry walks towards Caitlin and Cisco, when Savitar, in a rage, attempts to strike at Barry, but he is shot in the back by Iris. After that, he is erased forever.
A private funeral is held for H.R., where Iris holds a eulogy. Caitlin is not among the others, but she is spotted nearby. Barry, Cisco and Julian attempt to get her to come back, but she refuses, and reveals she didn't take the cure. She claims she isn't Caitlin anymore, nor Killer Frost. She decides to leave to find out who she is, alone, and others don't make an effort to stop her.
In their apartment, Barry and Iris are laughing, when they shouldn't. Iris reveals she had wedding invitations made some time ago, but didn't send them as she wasn't sure, if she would be alive. Barry speeds them to the recipients in two seconds. As they are about to find happiness, an earthquake like phenomena strikes the city. The team is at S.T.A.R. Labs in order to learn, what is going on. Jay finally realizes, it's the Speed Force Prison. Without a speedster inside it, the Speed Force has become unstable. Barry realizes, that he must go to the Speed Force in order to stabilize it. In front of the S.T.A.R. Labs, Speed Force lightning strikes everywhere. Iris says, he can't go, as he will face hell if he goes, like Wally and Jay did. A Speed Force breach opens, and Nora Allen-avatar comes out, reassuring that Barry won't be going to hell, but like every speedster, he has reached his finish line. Barry says hearty goodbyes to everyone and enters the Speed Force.
- This episode aired on May 23, 2017, which was the date on which Savitar originally killed Iris.
- Savitar mentions DeVoe as he recalls his memory in S.T.A.R. Labs. This is a reference to Clifford DeVoe, a villain known as The Thinker. This is the second time a reference on DeVoe was made, the first being in "" by Abra Kadabra. Savitar stated that it "hadn't happened yet", foreshadowing the appearance of The Thinker in Season 4, where he is the main antagonist.
- This reference would first become significant in the episode Season 4 episode "", when new ally Ralph Dibny makes a reference to having been hired by 'DeVoe'; Barry is only aware of the significance of the name due to Savitar and Abra Kadabra having also mentioned the name.
- Savitar mentioning DeVoe is quite similar to when Ra's al Ghul mentions Damien Darhk in the Season 3 finale of ; both Ra's al Ghul and Savitar are the cult-leading, god-like main villains for the third seasons of both The Flash and Arrow while DeVoe and Darhk would go on to become the main antagonists of the fourth seasons in unusual way: Darhk is the first magical villain of Arrow and DeVoe the first non-speedster villain of The Flash. Both villains also reveal themselves in the fourth season premieres.
- Cisco refers to Savitar as "Two-Face" after being rescued by Gypsy. This is a tongue-in-cheek reference to the comics villain Harvey Dent aka Two-Face, an antagonist of Batman who also has severe scarring on half of his face.
- The story of his family that Barry talked to Savitar about could be a reference to the beginning of the animated DC movie Justice League: Flashpoint Paradox. This storyline was also the catalyst for Season 3.
- A quote from Mark Twain appears on H.R.'s tombstone.
- Cisco asks Wally to "reverse the polarity on the neutron flow", referencing a catchphrase of the Third Doctor in Doctor Who; "reverse the polarity of the neutron flow"
- Hunter Zolomon's current form has been named as Black Flash by Savitar.
- Hunter's death is similar to that of Amaya's in "" in Season 2 of .
- The scene where Savitar is vibrating his hand while preparing to kill Cisco and telling him that he will die "the same way twice" refers to the latter's death in the erased timeline in "".
- Savitar is killed the same way that The Rival was killed in ""; The Rival was shot in the back by Joe while trying to attack Barry from behind, and Savitar was shot in the back by Iris when trying to do the same to Barry.
- The Speed Force lightning storm above Central City is a reference to a similar storm that appeared in the first issue of the 2016 Flash relaunch comic that infused several citizens with the Speed Force. It's now known that the one seen in the episode has similar abilities to potentially create new meta-humans.
- This episode is set after the Season 2 finale of , "", given that Black Flash appeared in that episode to kill Eobard Thawne, and is killed in this episode.
- This is the third time that Barry went into the Speed force, the first time being in the episode "" and the second time in "".
- This is the last episode of the series to use the original title card used since Season 1.
- In the previous episode, H.R.'s last words to Cisco are "'Til next time" and he salutes the latter after putting on his hat. However, in this episode, the flashback shows it was changed to "'Til the next one" and H.R. slightly tips his hat.
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