With Doom (Tony Todd) closing in on "The Flash," Barry Allen (Grant Gustin) is going to need some help. So, it is more important than ever for the Flash to have a working Firestorm. That means saving Dr. Stein, who collapsed in a cloud of blue flames at the end of episode 3. What would they do in episode 4, "The Fury of Firestorm"?
The episode begins at a high school football game where Jax Jackson (Franz Drameh) is a star in the making. College recruiters fill the stands at the big game. However, it is the night of the particle accelerator blast and Jax is hurt in the explosion.
Fast forward to the present at S.T.A.R. Labs, where Cisco (Carlos Valdes) has stabilized Dr. Stein with the power source in Wells' (Tom Cavanaugh) old wheelchair, but it will work only for a few days. If they are going to save Stein, they need to find another potential Firestorm partner to bond with Stein's mutated molecules. Caitlin (Danielle Panabaker) cross-references the records of people affected by the particle accelerator blast with genetic matches for Stein. She gets two potential matches -- Jax Jackson from the football game and a scientist named Dr. Henry Hewitt (Demore Barnes).
Barry and Stein go to visit Jax, who is now a mechanic. He lost his chance at a football scholarship when his knee got injured in the particle accelerator blast. They try to convince him to come back to S.T.A.R. Labs for tests under the premise they can fix his knee. However, Jax says he does not talk about that night anymore because of what it did to his family. Barry and Stein leave disappointed, but Barry leaves Jax his card.
Meanwhile, Joe and Iris meet with Francine (Vanessa Williams). To Joe's surprise, Iris has agreed to see her mother. However, when they all actually sit down she shocks him with her decision. With a steely resolve, she tells Francine that she does not want them to get know each other.
"I can appreciate you feeling like this is suddenly the right time for you to want me in your life, but that does not mean it is the right time for me," Iris says. "We have lead separate lives for more than 20 years. Let's keep it that way."
Back at S.T.A.R. Labs, Caitlin has found Hewitt who readily agrees to join Team Firestorm. He and Stein instantly hit it off -- Hewitt is a fan of Stein's work and, even though Cisco says Hewitt has an ego, everyone is excited for the possible match. Unfortunately, when Cisco wires Hewitt up and Stein tries to bond with him nothing happens. They are not compatible. Hewitt is angry. He feels that Caitlin falsely built up his hopes. He storms out of the lab, but curiously when he hits the button for the elevator his hand catches fire.
Meanwhile, over at Mercury Labs, there has been a break-in in the applied sciences department -- It's Dr. Wells, well Dr. Wells from Earth 2!
The next day Joe and Patty (Shantel VanSanten) show up to investigate the break-in. When he finds out Dr. Wells was seen pulling off the caper he is spooked. Wells tells Patty not to tell Barry about Wells. He tells her that Wells killed his mom so it would only bother him. She warns him she is bad at lying.
"Well, you better learn fast," snips Joe.
Later, Francine shows up at the police station. Joe is angry that she has not left town, but she has something else to tell him -- she is dying. She begs him to make Iris reconsider meeting.
Jax shows up at S.T.A.R. Labs, suddenly curious if they can fix his knee. However, when they spill the beans about Firestorm, he bolts. He has no interest in being a superhero. Caitlin is furious. "Who would say no to being a superhero," she asks -- Cisco awkwardly dodges that question. Barry says it takes time to process, but Caitlin reminds him they do not have much time.
Back at the police station, Barry gives Patty some bad news. She had given him teeth to test under the theory that they were from some land shark meta-human (foreshadowing!). Barry tells they are regular, old human teeth. They flirt. You can cut the romantic tension with a knife, but nothing happens. Afterward, Barry tells Joe he is holding back. "She is just not Iris," he confides. Joe tells him that Iris is his first love and he will never feel the same way about anyone else, but not to let that stop him from exploring something new.
With Stein's health deteriorating, Caitlin goes herself to convince Jax to join S.T.A.R. Labs. She tells him about Ronnie (Robbie Amell) and promises he can find purpose being a part something bigger than himself. Her pitch is interrupted when Hewitt shows up. He is not stable, emotionally or molecularly. The attempt at bonding with Stein has turned him into a fiery meta-human and he is out for revenge. Iris and Jax barely escape alive.
They show up at S.T.A.R. Labs just in time for Jax to merge with Stein and save his life. Together they become Firestorm and Jax is loving it -- he even has a nickname for Stein: Grey. However, the duo does not have time to celebrate. Firestorm and the Flash are needed at the football field where Jax was injured. Hewitt is there causing chaos with his flaming rage. They realize angering Hewitt intensifies the fusion in his body. They taunt Hewitt in an attempt to basically overheat him. It works. They have the making of a fantastic new team.
"Welcome aboard, Firestorm," Barry says.
Elsewhere, Iris meets with her mother again in light of her health issues. She tells Francine she was relieved to find that her mother was not lying about dying. However, Francine was keeping one big secret: She had another child eight months after leaving Joe and her behind. She grills her mother about her possible brother -- fans had better get ready for Wally West! The conversation ends, though, with Iris telling Francine to leave for good.
Barry, Joe, Cisco, and Caitlin gather to see off Jax and Stein. They are headed out of town for some Firestorm training. Stein gives Cisco some parting advice to make use of the gift of his emerging powers. Joe notes that Barry should learn from Jax's big leap of faith and make a move on Patty.
Barry goes to the police station to do just that, but instead he finds King Shark! It looks like Patty was not wrong after all. Patty comes outside to find Barry, still in his Flash costume, in King Shark's clutches and tries to help. However, a mystery man ends up shooting and stunning the meta-human and saving both of their lives. Barry chases after the hooded figure who reveals himself to be Wells! Barry was not expecting that!