The finale opens with the same monologue we’ve heard all season, albeit in a somber tone. Everyone watches Barry as he descends into the particle accelerator where he confronts Dr. Wells. Barry finally gets to ask the question he’s wanted an answer to this whole time, why did Thawne kill his mother? It’s simple, because he hates him. Wells then goes over his entire plan from the beginning for those that haven’t been watching the show – how he came from the future to kill young Barry but decided to torture him with an existence of suffering by killing his mom and then lost his way home. He goes on to tell Barry that despite going through those motions, he needed Barry to become fast enough to create a wormhole and send him home. Dr. Wells makes the offer Barry can’t refuse, help him and he’ll help Barry reunite the Allen family, and a chance to undo all his evil.
Later, Dr. Stein goes over the risks of Barry actually going back in time, which could amount to serious changes. Barry weighs the good and the bad of it – he’d have his mother but he’d have never grown up with Joe or Iris, etc. Joe throws his support behind Barry carrying it out and leaves, Barry follows him and Joe says it’s time Barry had a chance to save himself. Afterward, Barry goes to see his father and tells him about the opportunity he has. Henry tells him not to do it, that everything happens for a reason and he would care if Barry was fundamentally altered because of this decision. He even plays the “your mom wouldn’t want that” card and hopes that Barry becomes a dad one day so he knows how much he loves him.
Back at STAR, Ronnie reveals to Caitlin that he and Dr. Stein are back in town for good now and that he’d finally like to make her a proper woman. At Jitters, Barry contemplates on the roof, where he is joined by Iris, who asks him what he’s going to do. He thinks about the consequences of it, because if he’s wrong he can’t undo any of it. Iris goes over all the reasons for him to do it, even acknowledging that she knows of their impending marriage. Reluctantly, Barry admits how hard it was for him to admit how he felt having grown up with Iris, but he has had a great life despite waiting too long. Barry asks Iris what she thinks he should do, and she echoes Joe: he should do what he needs to do for himself. Having made up his mind, Barry goes to see Dr. Wells to ask how it all works. Wells says they use the particle accelerator, but instead of two particles they use one, with which Barry will collide and punch a hole through the fabric of reality, opening up this time to infinite times (Crisis on Infinite Earths anyone?). If he fails though, he’ll die.
As Dr. Stein re-explains the science for the audience members not paying attention, Cisco starts to question why Barry would even consider doing this. Stein reveals that Barry would have to be traveling at Mach 2 speeds (well over 1500 miles per hour) and if it doesn’t go as planned he’ll be like a bug on a windshield. Barry reveals to Cisco the second part of the deal, helping Wells go home. Luckily, Wells has blueprints and has been gathering the supplies for his time machine. There’s a problem though and Cisco has to go get advice from Wells once again. Dr. Wells tells Cisco how to fix the problem, and Cisco finally confronts him about killing him in the alternate timeline. Wells apologizes, not for killing him but because he remembers. He also drops the nugget that Cisco was effected the night of the particle accelerator explosion, and he would do well to remember who gave him that gift.
Dr. Stein continues to make calculations as Eddie stands with his hands in his pockets, since Dr. Wells convinced him he doesn’t actually matter. Though they are surrounded by all manner of scientific ideas, the sheer coincidence that Eddie exists in the timeline that his distant relative does makes him an anomaly. Stein tells Eddie he gets to choose his own future now – it’s the theme of the episode kids! A computer begins to bleep loudly which prompts Stein to address everyone else: Dr. Wells didn’t tell them everything, colliding with the particle could create a black hole that could destroy the planet. The group speaks with Dr. Wells, who reminds them that he’s been helping them all this entire year and that he’s been planning this for decades. It will all work, but Barry will have just 1 minute and 52 seconds to do what needs to be done.
Barry and Joe chat in the room with the treadmill, and Joe admits he’s clueless about what Barry should do. He’s got total confidence in him pulling it off though. For his entire life, Barry has dreamed about saving his mother, but he didn’t anticipate losing another parent over it, but Joe reassures him he won’t be lost. Across town, Eddie goes to see Iris at CCPN and tells her the story of a canceled date that lead to him arresting the mugger that took her bag (way back in the pilot!). The power of that coincidence convinced him, screw the future, and Iris agrees. Later in front of STAR, Dr. Stein marries Ronnie and Caitlin, having learned a lot about merging lives together that year. Caitlin believes that all the events of that year have lead to this. Everyone is happy, except Barry who continues to ponder his choices.
It’s time. Everyone offers Barry support as he prepares to make the trip. He and Joe share a particularly intimate moment where they call each other “Dad” and “Son.” Iris kisses him on the forehead and wishes that whatever life he gets is enough for him. Barry goes inside and Wells delivers his token “Run Barry, Run” line, and he does. As he gets faster, Barry connects with the speedforce and begins to see moments from all throughout time including: himself as a kid, Caitlin as the villain Killer Frost, a statue of him in front of the “Flash Museum,” what looks like himself in prison, a clip from the upcoming “DC’s Legends of Tomorrow,” and then finally, the moment he was looking for. Dr. Stein’s coffee begins to float and they inject the particle, Barry collides with it and the wormhole is created. They start the timer.
Barry appears in his own room 15 years ago, then hears the rumpus. He watches from another room as his mother screams, and he and the Reverse Flash battle. Future Barry tosses the Reverse Flash out a window, then holds his hand out and shakes his head at Present Barry, warning him not to do it before running away with little Barry. Present Barry approaches his mother and comforts her. She tells him he looks like her father as he takes his mask off, and he tells her who he is, that he got a second chance to say bye, that he and his dad are okay and they love her. She tells him how beautiful he is before taking her last breath.
Back in the present, the clock counts down and it’s time to send Dr. Wells away. He admires their work on the time machine, saying Rip Hunter himself would be proud (the time traveler set to appear in “DC’s Legends of Tomorrow”). The wormhole spits out a silver helmet with little gold wings (the very helmet worn by the original Flash Jay Garrick) and when Cisco asks what it is, Wells says it’s his cue to leave. Wells closes his Time Sphere and prepares to go home, but Barry fires out of the wormhole, fist forward, and destroys the machine. Distraught, Wells asks why didn’t Barry save his mother, he could have everything he ever wanted, but Barry says he already does. Wells pulls his mask on and they have a speedster throw down.
Dr. Stein warns the others to cut the generators in order to stop the black hole. Ronnie gets zapped in the process but Caitlin cuts it off and closes the hole. The Reverse Flash pins Barry down and tells him he’s going to kill everyone in there after he kills him, because he always wins. Then something he couldn’t have thought of happens. Eddie, his ancestor, takes his own life. Wells starts to vibrate all crazy like before shifting back into the original Eobard Thawne. Eddie gasps for breath, saying he’s a hero after all, and he only ever wanted to be Iris’s hero. As Eddie dies, the Reverse Flash begins to break away into dust, but not a beat passes before the wormhole opens again. Barry carries Cisco, Joe and Iris out, though she protests, and the black hole begins to grow and sucks up Eddie’s body.
The black hole continues to grow, and hovers over Central City, pulling up concrete and parts of buildings. Citizens begin to watch including Captain Cold, Captain Singh, Henry Allen, and even the yet-to-be-shown Hawkgirl. Dr. Stein reveals they can disrupt the motion of the singularity by traveling in reverse. Lucky for all of them, Barry is a hero and takes on the challenge without a second thought. He races up a building, hopping from hunk of debris to another and leaps directly into the hole.