Tonight's episode picks up immediately after the events of last week's episode, Barry is still holding Iris is his arm as Joe and Tracy Brand
Iris gasps and she holds HR's face-transforming device up to her face — it's revealed that HR and Iris swapped places and HR was the one stabbed by Savitar.
In a flashback sequence, it's shown that HR felt guilty enough about revealing Iris' location that he swapped places with Iris to make the ultimate sacrifice.
Back in real time, HR and Tracy share a brief moment where HR confesses his love for her. Before passing away, HR whispers something to Barry and tells him to tell Cisco. Before taking his last breath, he tells Barry to "go stop Savitar."
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Joe runs to Barry and Iris to tell them that Savitar took the Speedforce bazooka. We see Killer Frost and Cisco in the forest about to fight. Savitar speeds in and tells Killer Frost not to kill him because he needs Cisco's helping building something.
Savitar then realizes that Iris wasn't the one murdered.
The group reassembles at STAR Labs and begin talking about the paradox created when Savitar killed HR instead of Iris. Barry tells the group it could take upwards of a few hours for Savitar to be erased because of the paradox. Julian then shares with the group that he had worked with Caitlin's mother to come up with a cure for Killer Frost.
Wally races in and tells the group that Savitar has taken both Killer Frost and Cisco. We find out that Savitar wants Cisco to make adjustments to the Speedforce bazooka that would allow Savitar to have time remnants throughout time, all sharing the same consciousness.
Savitar has a vision of Julian finding the cure for Caitlin and proceeds to tell that to Cisco, using it as leverage to get him to work on the updates to the Speedforce bazooka.
In the original Harrison Well's former Reverse Flash suit room, Barry and Iris share their first alone moment after the incident. Barry tells Iris that he'd do the "last thing she expects" to stop Savitar.
Barry confronts Savitar and informs him that the two can stop hurting each other. Barry begins sharing memories the two took part in and Savitar reveals he stills shares the same memories.
In the next scene, Barry shows up to STAR Labs, and he's brought Savitar along. Savitar thinks that Tracy Brand is his only hope, and she refuses to help him saying that he "took away her future." Iris says she has an idea of somebody that might be able to get Tracy to help.
Tracy is in her room staring at the whiteboard when she catches the reflection of Harrison Wells in the board. She turns around and Harrison explains that he's HR's doppelganger from a different Earth in the multiverse, before proceeding to give her a talk on why she must use HR's death to help stop Savitar.
While Barry, Savitar, and Iris are having a conversation about their respective futures, the STAR Labs alarms start going off. They race into the main room and see that Savitar has rigged the Philosopher's Stone to explode. Wally and Barry evacuate the team to safety.
Cisco tells Killer Frost he's finished with the adjustments to the Speedforce bazooka just as Savitar speeds in. Savitar instructs Killer Frost to kill Cisco and just as she shoots ice picks towards Cisco, Gypsy appears and the two vibe to safety.
Savitar and Killer Frost then travel to the waterfront where they begin the plans on making Savitar immortal. As Savitar uses the Philosopher's Stone to open up the Speed Force, Black Flash appears to kill Savitar, only to get frozen by Killer Frost. Killer Frost then uses the Speedforce bazooka on Savitar in hopes of making the time remnants.
In the midst of the process, Savitar is knocked over by a speedster revealed to be Jay Garrick. Barry, Wally, Cisco, and Gypsy show up with Jay to take on Killer Frost and Savitar. Savitar speeds off, pursued by the speedsters while Cisco and Gypsy stay behind to fight Killer Frost.
Savitar speeds back and picks up Cisco, about to kill him when he's stopped by Killer Frost. Barry speeds back into the scene and Savitar tells him that although he only has a few minutes left, he plans on killing Joe, Iris, and Wally.
Barry manages to get Savitar out of his armor and destroys it. While walking back to Caitlin and Cisco, Savitar tries sneaking up behind Barry to kill him when we hear a gunshot, Iris killed Savitar.
The group gathers around HR's funeral to pay their final respects. Barry pulls Cisco aside to tell him what HR whispered as he died: "Tell Cisco that this took strength and that he gave it to me."
She tells them that she's neither Caitlin nor Killer Frost, and she needs to go out on her own to find out who she really is.
Back at the West-Allen residence, Barry and Iris start talking over wedding plans. As the two lean in for a kiss, tremors start rocking Central City. They look outside the window, and it appears that lightning is striking all around Central City.
At STAR Labs, they come to the conclusion that it's a Speedforce storm because there's no one in it to stabilize it. The group runs outside and Barry
A new portal opens up and Barry's mother walks out, she says it's time for Barry to rest and finish his race. Barry walks around and says his final goodbyes to the group. Talking to Iris, he makes her promise that she'll always keep running and then he joins hands with his mother as the two venture into the Speedforce.
The portal closes and the storm instantly stops. Joe and Iris look at each other as a tear rolls down Iris' cheek.
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