Two years ago, a High School football player named Jefferson “Jax” Jackson celebrates a game winning touchdown with his friends and coach on the field. Football is clearly Jax’s chance at college. Suddenly, Jax sees in the distance the particle accelerator explode. He yells for everyone to get inside the stadium. One of his friends, who is on crutches, falls and Jax helps him up. They get inside, but before Jax can slam the door he is hit by the explosion and thrown into the wall.
Back in the present at S.T.A.R. Labs and in the present, Cisco, Caitlin, and Barry all try to stabilize Stein, who is having a sort of convulsion. Cisco manages to power up the Firestorm stabilizer with the power source from Well’s wheelchair, but it is almost drained and won’t work for more than a few days.
Caitlin theorizes that this happening to Stein because the dark matter from the singularity damaged the Firestorm matrix. He needs to bond with Ronnie, which of course is impossible. Caitlin has come up with two potential replacements, young men who were also affected the right way by the particle accelerator explosion and who match Stein’s blood type. One of them is Jax, who now works as a mechanic. The other is a scientist named Henry Hewitt. Barry speeds to both their work places and gets blood samples without them realizing it.
At Joe’s house, Iris looks at baby pictures of herself with her Mom. Joe walks up and tells her a story behind one photo. He tells her that she does not need to meet her mother the next day, but she wants to go.
At the police station, Patty asks Barry to look at some shark teeth for her. Apparently there was a report of a man-shark and she thinks it is a new metahuman. Barry is skeptical of an actual half man, half shark. He also tells Patty that he is not really into researching metahumans, but does agree to run some tests to help her out. Joe come in at that point, and when Patty goes to check for more clues about the possible man-shark, Joe calls Barry out on flirting with Patty. They are interrupted by a text from Cisco.
At S.T.A.R. Labs Stein is awake, and using a cane Cisco made with the power source inside. Caitlin has finished testing the blood, and both men are still candidates. Caitlin is especially excited about Hewitt, since he is a scientist. But Barry points out that Jax is a closer match, and more physically built, plus also intelligent with a GPA of 4.0. They decide to meet both men, and Caitlin goes to make contact with Hewitt while Barry and Stein head out to meet Jax. Cisco also heads off to do some work, unaware he is being followed by Wells.
At the garage, Barry claims that he and Stein work for a brand new Department of Safety. They want to talk to Jay because they are collecting data on the particle accelerator explosion. Jax refuses to help. He refuses to talk about that night, because the injuries he sustained ruined his chances at playing football. Barry leaves his number, in case Jax changes his mind.
At Jitters, Francine and Joe wait. When Iris arrives, she hugs Joe, but is clearly uncomfortable when Francine holds her hands. Iris wishes her mother the best, but says she and Joe have been fine without Francine for twenty years and does not want that to change. She tells Francine she wants them to stay apart and leaves.
Hewitt is at S.T.A.R. Labs, incredibly excited by everything Cisco and Caitlin have told him about being Firestorm. He can’t wait. When Barry and Stein enter, Hewitt is even more thrilled to meet Stein, who he calls a legend. Caitlin is thrilled, though Barry is still unsure and Cisco has noted Hewitt has an ego. Since Jax refused to talk to them, they decide to try anyway. Cisco puts the stabilizer on Hewitt. When Stein and Hewitt touch hands, there is a few seconds of fire, then nothing. They try again, but it does not work. Hewitt is not a close enough match. He is furious at them for getting his hopes up and storms out. As Hewitt reaches the elevator, there is flame around his hand. But he doesn’t notice.
At Mercury Labs that night, Amanda Palmer is talking to her assistant when they hear a noise. They go to check it out, and come across a thief. Palmer recognizes the thief as Harrison Wells, who walks out before he can be stopped.
The next day, Joe and Patty arrive at Mercury to investigate the break-in. Palmer reveals that the thief was Wells, and that he was walking. Patty wants to fill Barry in right away, but Joe tells her no. He explains that Wells killed Barry’s mother and asks her not to tell Barry about this.
Francine is waiting at the police station when Joe and Patty return. Joe tells her to leave, that Iris made it clear she does not want Francine around. Francine admits that she is dying from a disease called McGregors, a side effect of her previous drug use. She only has until the end of the year at most.
Jax comes to S.T.A.R. Labs after all, assuming they might be able to fix his injured knee. Barry, Caitlin, Stein, and Cisco explain the truth about Firestorm to him. Jax is shocked to learn he is a metahuman and decides to leave, calling them crazy. Caitlin gets angry and demands to know why Jax didn’t go to college, even with his good grades. She assumes he quits when things don’t go his way. Jax leaves, and Caitlin wants to try Hewitt again,
In Barry’s lab at the police station, he tells Patty that the teeth she found are human. There’s no man-shark. She mentions having another case anyway, and awkwardly fumbles her way around his questions of it, mentioning that Joe didn’t want her to tell Barry.
Barry finds Joe in the station, and Joe fills him in on what is happening with Francine. Barry asks about Joe and Patty’s new case, and Joe (much more smoothly than Patty) covers and shifts the conversation to Barry and Patty. Barry admits Patty is great, except she is not Iris. Joe encourages Barry to try something new.
At work, Hewitt angrily watches news footage about Flash Day. Another scientist comes in, needing something from Hewitt, but it is not ready yet. The scientist is angry, apparently Hewitt is unreliable. When he threatens Hewitt’s job, Hewitt yells angrily, flames forming all over his body.
Barry, Caitlin, Cisco, and Stein watch the news at S.T.A.R. Labs, the lab where Hewitt works had an explosion and Hewitt is a suspect. They theorize that they woke up his metahuman abilities after all. Cisco reveals that he did some hacking and discovered that Hewitt has a sealed police record, all his crimes have been violent and he’s been sent to anger management. Stein isn’t feeling well, so Cisco helps escort him away to rest.
Caitlin blames herself both for Hewitt and for them losing Jax. Barry tells her that she chose not to see what was in front of her. Echoing Joe’s advice, he suggests she explore something new.
At Joe’s house, Joe’s told Iris about Francine’s illness. Iris thinks it is a lie, but Joe is sure she is telling the truth. Iris still isn’t sure about seeing her mother, and Joe offers to support her no matter what choice she makes.
Caitlin goes to the garage to apologize to Jax. She tells him about Ronnie, and how he died. Jax explains that without a football scholarship, he couldn’t afford college. Caitlin tells him that the particle accelerator took, but it also gave. “I believe you were meant to be a hero.”
Hewitt suddenly walks in, he’s been looking for Caitlin. He uses his new powers to throw Jax aside. Hewitt blames Caitlin for how he is now, but Jax throws something at his head and knocks him down before Caitlin can get hurt. Jax and Caitlin escape.
Stein is in bad shape, the power source is out and he’ll die if he doesn’t merge soon. Seeing this, Jax agrees to help. Caitlin helps Jax with the stabilizer while Barry and Caitlin help Stein stand. It works, they merge into Firestorm at once. Before Jax even has a chance to get used to it, the alarm sounds. Hewitt is gathering energy at the High School football stadium where Jax got hurt.
Players and spectators run for cover as Hewitt takes power from the stadium. Cisco shuts the power off to stop him. The Flash and Firestorm face Hewitt, who is furious when he sees that Jax got what he wanted. Jax struggles a bit at first, but Stein coaches him. The Flash tells Caitlin and Cisco that Hewitt seems to be charging up just on anger. Caitlin realizes if he gets mad enough, Hewitt will burn out.
The Flash speeds around Hewitt, dodging him and making Hewitt angrier. Both The Flash and Firestorm taunt Hewitt, saying whatever they can to make him mad. It works, Hewitt lets out a huge burst and then loses his power. Firestorm knocks Hewitt out. Stein is pleased with how well he and Jax work together.
Iris meets Francine at Jitters. Iris explains that she looked into Francine because she doesn’t believe her, and knows the disease is real. Francine assures Iris that she would never lie about something so big. This infuriates Iris, who reveals that in her investigation, she learned Francine had a son 8 months after leaving. Iris is furious that her mother is still hiding things, and says she never wants to see Francine again. And that Joe can’t know that he might have a son who grew up without him.
Outside Stein’s home, the gang gathers, revealing that Hewitt is now powerless and contained in the pipeline until they are sure he will stay quiet. Stein and Jax are going to Pittsburg to train together. Caitlin gives Jax Ronnie’s compass as a goodbye present. And Stein once again tries to encourage Cisco to tell his friends about his metahuman ability. Once the goodbyes are done, Stein and Jax merge and fly away. Barry and Joe walk off together, and Joe again encourages Barry to ask Patty out.
At S.T.A.R. Labs, Caitlin replaces Ronnie’s computer file with Jax’s.
That night, The Flash watches Patty in the window at Jitters. Before he can do anything, something grabs him.
It’s Patty’s man shark, King Shark, who holds The Flash by the throat with one fin and tells him that Zoom sent him to kill The Flash. Patty sees them and shoots at King Shark, who is unaffected. Suddenly, King Shark is hit from behind with an energy weapon and falls. The person holding the weapon wears a hoodie so they can’t see his face.
The Flash speeds off with the man in the hoodie until they are alone, then demands to know who it is. He lowers the hoodie and turns around. It is Harrison Wells.