The episode begins with Barry going on a romantic date with Linda Park (Malese Jow). Meanwhile, Ronnie Raymond (Robbie Amell) confronts his old professor, Quentin Quale (Bill Dow). Raymond pleads for Quale’s help, since he knows all about explosives.
Cisco Ramon (Carlos Valdes) is pulled away from a casual meeting with Barry and Caitlin Snow (Danielle Panabaker), in order to meet up with Detective West (Jesse L. Martin). The pair return to the house, where Barry’s mother was murdered. Joe insists he believes he knows who is responsible for her death. The pair are startled, when Sherry (Chase Masterson) opens the door. She seems a little too eager to let them in, after confirming she is divorced.
At STAR Labs, Dr. Harrison Wells (Tom Cavanagh) speaks to Caitlin and Barry about Raymond, who has been on a path of destruction through the town. The show flashes back to the day of the particle accelerator explosion, when Barry spoke with Dr. Martin Stein (Victor Garbar) on the train. The pair discuss Wells and the accelerator, before Barry departs. Afterwards, Wells and Barry pay a visit to Martin’s wife, Clarissa (Isabella Hofmann). Clarissa is questioned about her husband’s disappearance. Although she has no info on his whereabouts, she admits to knowing Ronnie. We see Martin’s behavior, after learning he has taken over Ronnie’s body.
Meanwhile, Joe and Cisco continue their investigation, when Sherry enters and attempts to bribe the men, with drinks. They learn everything has changed except for a single mirror. Cisco insists the mirror might show images of what happened on the night of the murder. That night, Barry enjoys another date with Linda. The pair get hot and heavy, when Wells and Caitlin witness Ronnie arriving home. After breaking the bad news to Linda, The Flash arrives and attempts to stop Ronnie. Eventually, Ronnie gets the chance to burn Barry, but Caitlin’s presence stops him.
Using a high-tech machine, Cisco and Joe are able to replay the events of the murder. They discover bloodstains all over the wall, when the wallpaper is removed. Joe suggests it belongs to one of the speedsters. Barry apologizes to Linda. Afterwards, Iris (Candice Patton) convinces Linda it is best to give Barry time and that he isn’t ready for a relationship. Using the tracker Barry put on Ronnie, they’re able to track him down. Clarissa is able to convince Martin that the people at STAR Labs can help him.
At the lab, the group prepared to run tests on Ronnie, when Barry receives a call from Linda. She tells him it is best to take some time apart, since Iris told her he was hung up on her. Barry confronts Iris and insists he no longer has those feelings. Joe and Cisco discover two different blood samples. Joe suggests running the samples against Wells’s. The pair argue over the accusation, before Cisco leaves.
Wells discovers that Ronnie’s body is rejecting Stein and both will die, unless they kill the host body. Caitlin insists the group has a few hours to come up with a solution and should use them carefully, before rushing to drastic actions. Barry returns to Linda and threatens to eat the world’s hottest pepper, if she doesn’t agree to go on another date with him. He is forced to eat the pepper, but she eventually agrees and it is sealed with a kiss, but Iris doesn’t seem too pleased.
Wells retrieves a gun, before returning and suggesting they have a new ideal. Cisco enters and tells the group Stein is gone. Wells and Cisco make a quantum splicer, which Barry and Caitlin plan on using to save Ronnie and Stein. Joe calls Cisco and learns the sample didn’t come back to Wells, but did for Barry. Cisco insists the samples are from an adult Barry. Barry and Caitlin stop Stein’s suicide attempt. The quantum splicer doesn’t work and Barry is forced to flee with Caitlin. After the explosion, General Wade Eiling (Clancy Brown) is made aware of the situation, before he plans his move.
The Nuclear Man was an excellent episode, because it moved the story further, without a needless side story. Instead, the entire forty minutes focused on the hunt for the killer of Barry’s mother and the looming death of Ronnie Raymond and Stein. Of course, it was also fun to witness Iris in Barry’s previous situation. Let’s just hope he doesn’t want anything to do with her, but he likely will. The episode deserves an 8.5 out of 10.