Barry confronts the imprisoned Harrison, who invites him to ask his questions. He says that he was born 136 years from the present, and tells Barry to ask what he really wants to know. Barry asks why he killed Nora, and Harrison says that their enemies in one possible future. Neither one of them was strong enough to beat the other until Harrison learned Barry's secret identity. He set out to travel back in time and kill Barry as a child, wiping out his future self. However, the Flash followed him back and moved his younger self out of the house. Harrison figured that if Barry suffered something traumatic enough then his child self would never recover, and never become the Flash. However, he then discovered that he had lost his ability to harness the speed force, trapping himself in that time. The only way back was the Flash, so Harrison created him using the particle accelerator.
Barry wonders why Harrison helped him to become faster, Harrison says that he needed him to become fast enough to create a stable wormhole so he could return home. When Barry asks why he would do that, Harrison says that if he does then he'll give him what he wants: the chance to go back and save his mother. Barry doesn't believe him and angrily says that he wants to kill him, and Harrison admits that he's proud of what he's taught him. He asks Barry if he wants the chance to undo all of the evil that he's done, and Barry walks away.
Barry tells the team, Martin, and Ronnie about Harrison's offer. Martin warns that Barry changed history once and this time he could do considerably more and never remember any of it. The professor warns that there's no way to know what Barry's life could be. Joe tells Barry that there's no choice and he has to change the past. He walks out and Barry goes after him. He wonders if Joe is okay with the fact that Barry won't live with him, but Joe points out that Barry will have a father and a mother to grow up with. The detective says that Barry has saved a lot of lives in the past year, and now it's time to save his own.
At Iron Heights Prison, Barry meets with Henry and explains Harrison's offer. When Barry says that Joe thinks he should do it, Henry says that Barry can't. He insists that there's a natural order to things and he believes that there's a reason for what happened. Henry points out that the timeline could change Barry, taking away the honesty and heart that he's acquired He says that Nora would say the same thing, and that he hopes Barry will become his father and then he will know how much Henry truly loves him.
At S.T.A.R. Labs, Caitlin checks Ronnie. Ronnie says that he's back for good to be with Caitlin. He reminds her that she agreed to marry him and says that they should finally do it.
Barry is up on the roof when Iris finds him. She asks if he's going to save Nora, and Barry admits that it's the biggest decision of his life. Iris reveals that she knows they get married in one future, and Barry admits that their living together may have changed it so they never marry. He assures Iris that he had a great life, and as they hug Barry asks what she thinks he should do. Iris tells him that for once in his life he should do what's in his heart and what he needs to do for himself.
Later, Barry goes back the pipeline and asks Harrison how it works. Harrison says that they use the accelerator it was designed to use. This time they'll only inject one hydrogen particle into the accelerator. When it collides with Barry, if he's going fast enough, he'll create the wormhole and travel back to the past... or Harrison's future. If he doesn't reach the required velocity, Harrison warns Barry that he'll die.
The team checks Harrison's calculations and Cisco wonders why Barry would ever consider doing it. Martin says that Barry will have to go Mach 2 at a minimum, and Caitlin warns that he's never gone that fast before. Barry says that he needs Cisco to help build a time machine.
Barry, Cisco, and Ronnie go to the lab and Barry says that Harrison will need a ship to travel into the future. Harrison has hidden the parts as he slowly built one. Ronnie confirms that the tiles are made of tungsten, which gives off flammable dust. Cisco gets an idea and goes to ask Harrison. Harrison confirms that Ronnie is right, and says that he wishes Cisco had been with him when he built the accelerator. He suggests that they cement the tiles with a cobalt resin, and then says that he thought Cisco would understand how he's trapped. Cisco says that Harrison killed him in the alternate timeline and he never forgot it. Shocked, Harrison says that he's now sure that Cisco was affected by the accelerator explosion as well. Cisco doesn't believe it, and Harrison says that a great and honorable destiny awaits him… and he should remember who gave that life to him out of love. Speechless, Cisco walks away.
In the lab, Martin asks Eddie to step away so he can use the console he's sitting at. Eddie figures that he's useless after what Harrison told him, and Martin wonders why he believed him. He says that Eddie might be the most interesting thing there and points out that the odds are against Harrison being stuck in the exact moment of time when Eddie was working. Excited, Martin says that Eddie is an anomaly--the only person among them who gets to choose his own story.
Once he runs the calculations, Martin tells Barry and the others that Harrison is holding back information. When Barry collides with the hydrogen particle, he could create a black hole singularity that could cause a global catastrophe. They contact Harrison in his cell and he admits that there's a risk. However, he points out that he's been fighting alongside all of them, and insists that it will work. Once the wormhole stabilizes, Barry will have one minute and fifty-two seconds in the past and then return, and they can close the wormhole. Barry realizes that he won't have enough time to stop Harrison, and insists that he believes in Barry and always has.
Barry goes into the treadmill room and Joe follows his foster son. Joe admits that he doesn't know what to think, and he doesn't want Barry to worry about him when he's saving Nora. Barry wonders if he's fast enough, and Joe insists that he is. Barry says that he never thought he'd have to lose one parent to get back two, and says that Joe has always been his father even if he hasn't always realized it. Joe assures him that Barr will never lose him.
Eddie goes to Picture News and brings takeout for Iris. He talks about before he met Iris, he had a date with another girl. She pulled a hamstring and had to call it off. Eddie was walking home when he saw the mugger with Iris' backpack, and that's how they met. He's realized how many coincidences had to happen for him and Iris to get together, and that he has a destiny as well... with Iris. He says to screw the future, and Iris agrees as they kiss.
Outside S.T.A.R. Labs, Martin officiates at Ronnie and Caitlin's wedding. They exchange rings and Caitlin says that she has everything she could ever need.
Back in the lab, Barry dons his costume and prepares to make his run. Cisco walks him through what he has to do once his future self takes his younger self out of the house. Barry says his goodbyes and Iris says that she hopes whatever life he gets makes him happy. The Flash enters the pipeline and Martin reminds him over the intercom that he only has one minute and fifty-two second. Harrison is waiting in his cell and tells the Flash that he can do it, and says to run.
The Flash speeds around the pipeline and the building starts to shake as Barry passes Mach 2. Harrison warns Barry that he's seeing the Speed Force: his past and future all at once. He tells the Flash to concentrate on his mother, and Martin injects the hydrogen particle. The wormhole stabilizes and they start the countdown.
Years in the past, the Flash materializes in his childhood bedroom. He hears his younger self crying to Nora and looks in as he sees his future self arrive and then shakes his head no. After a moment, the future Flash carries Young Barry out of the house, and Reverse Flash stabs Nora. The Flash closes the door and waits until the Reverse Flash has left. He goes into the room and finds Henry unconscious. Nora is dying, and the Flash tells her that her son and husband are safe. He merely says that he's the Flash and then removes his hood. Nora says that he looks just like her father, and Barry says that he's her son and he had a second chance to come back and tell her that he and Henry are both okay, and they love her. His mother says goodbye and dies.
As the countdown continues, Cisco and Joe escort Harrison to Cisco's Time Sphere. A metal helmet comes through the wormhole, and Harrison merely says that it's his cue to leave. He thanks Cisco, who tells him to never come back, and then enters the Time Sphere. The Sphere lifts up... and the Flash streaks back through the wormhole, shattering the Sphere.
Caitlin and Ronnie run to shut down the wormhole, while Harrison demands to know why the Flash didn't save Nora. The Flash says that he already has everything he wants, and Reverse Flash attacks him.
With ten seconds left, Ronnie and Caitlin try to cut the generators. An explosion knocks Ronnie back. Caitlin manages to shut down the power and goes to Ronnie.
Reverse Flash beats the Flash and says that once he kills Barry, he'll kill his friends and his father. Eddie arrives and shoots himself, and Reverse Flash steps back in shock. Joe runs to his partner and asks what he did, and Eddie says that there's no such thing as coincidence. Cisco realizes that if Eddie dies then Harrison will never be born. As Iris runs into the chamber and goes to Eddie, Harrison reverts to his original body. Iris assures Eddie that he's a hero, and he says that's all he ever wanted to be... and then dies.
As Eobard is erased from existence, he asks Barry how he'll get along without him after he's controlled so much of Barry's life. He disappears and the wormhole opens up, and Martin warns that it's reopening on its own. Barry and Joe pull Iris away and the wormhole sucks up Eddie's body and everything else in the area.
Outside, the group watches as a singularity opens. Martin warns that it won't stop feeding even after the earth is gone.
Across town, Captain Cold, Singh, Henry, and millions more watch as the singularity grows.
Martin says that the diffuse material is in orbit around the singularity. Barry realizes that they have to disrupt the motion, and Martin warns him that it can't be stopped. Despite that, Barry dons his mask and begins running as fast as he can around the singularity.
Written by Gadfly on Oct 2, 2015