The episode opens with the Flash and Caitlin outrunning the nuclear explosion set in motion by Ronnie Raymond and Professor Stein. Caitlin is worried about their exposure to radiation, but Cisco reports that there is no radiation whatsoever. With this news, they approach the blast site where they find Ronnie and Dr. Stein…alive and conscious. Both men are fully separated and appear to be okay. All four arrive at STAR Labs where they are greeted by Cisco and Wells.
Meanwhile the military moves in on the blast site where they notice the two imprints of two different people. General Eiling realizes that “Firestorm” has separated and that they need to find both men.
Meanwhile back at STAR Labs, Caitlin is excited to have Ronnie back. Both men seem to no longer have their nuclear powers. Both men however begin to argue about disagreements they had when they were joined together. Both men couldn’t be happier to be separated form each other. Dr. Stein is reunited with his wife who is thrilled to see him. After returning Stein home, he thanks Barry for bringing him home.
At the police department, Barry meets with Joe who tells him that he has something to show Barry. He takes Barry to his childhood home – the scene of his mother’s murder. Barry tells Joe that he hasn’t stepped foot in the house since the night his mother was killed. Joe shows Barry the mirror and the holographic image that Cisco was able to retrieve from it. Barry is shocked to discover his adult blood on the walls of the crime scene. Barry and Joe come to the conclusion that their were two speedsters meaning that The Flash was trying to stop Reverse Flash.
Barry and Joe bring this ordeal to Dr. Harrison Wells. He suggests that time travel is possible but problematic. If you travel back in time to change something, you are the cause of that event. Joe tries to wrap his mind around time travel, but Cisco mentions that he knows someone that can help them.
At the news station Iris and a fellow reporter talk about STAR Lab’s connection to Firestorm. The reporter believes that Wells wanted the accelerator to explode but needs more evidence as to what is taking place at STAR Labs. He has Iris look into investigating this further.
Later that night, Barry visits Dr. Stein’s house and inquires about a paper he wrote about time travel. Before they can get to that – Stein suddenly craves Pizza (Pizza is Ronnie’s favorite food, and Stein normally hates pizza. ). It turns out that Stein and Ronnie seem to be more connected then they think. After Barry runs to get him a pizza, they finally begin their conversation on time travel. Stein believes that time travel is possible. Barry tells Stein about his mother being killed and that he possibly traveled back and tried to prevent it from happening. Stein suggests that in a future date the Flash moves so fast that he must smash a hole in the space time continuum. Barry believes that he’s destined to fail because he will not be able to save her.
Caitlin and Ronnie decide to go on a date to the coffee shop to catch up. She tells him all of the stories that she has encountered so far. Ronnie suggests that they move away and start over. Caitlin, however, reveals that she found a new way to help people by working with Barry and wants to stay. Before they can finish their conversation, the coffee shop is ambushed by General Eiling. Ronnie and Cailtin make a run for it, but Ronnie ends up being held up in an alleyway by General Eiling an a bunch of his men. The Flash races to the scene and makes easy work of Eiling’s men. Eiling is prepared for the Flash and throws a kinetic bomb in the air which targets kinetic energy. A bunch of spiked shrapnel stabs Barry, which causes him to lay in intense pain. Caitlin pulls up in the STAR Labs van and picks up both Ronnie and Barry and they all make a clean getaway.
Bat at STAR Labs, Caitlin picks the spikes from Barry. The gang discovers that Stein and Ronnie indeed do have a connection. General Eiling is after both men for the Firestorm project. His objective is to create the ultimate human weapon used for military purposes. Professor Stein shows up to the lab and offers to help the group stop the General. Barry lets Ronnie and Caitlin stay at his and Joe’s house. Joe shakes hands with Ronnie as Iris walks through the door. Caitlin makes up a lie saying that Ronnie is her cousin and that there is a gas leak in her apartment building and that is why they are staying at Joe’s. Iris says that she recognizes Ronnie from somewhere but can’t put her finger on it. She shrugs but remains suspicious.
Wells decides to pay Eiling a visit and asks why he is hunting both Ronnie and Stein. Eiling tells Wells that both men fuse into Firestorm and are the key to the future of warfare and weaponry. He also reveals that he knows that Barry is The Flash. Eiling tells him to turn over Ronnie and Stein – because they work well together. Wells seems to know that Eiling is holding all the cards.
Barry sits at home an admires a picture of his mother. Joe wonders if he made the right choice in telling Barry about the new evidence he discovered. Joe tells Barry that he is still his guardian and that he will always be there for him. He regrets handing Barry another burden, but Barry says that they will carrying it together. Barry asks Joe how he matched Barry’s blood to the blood on the Walls. He comes to the conclusion that Joe was trying to see if Wells was involved. Barry still doubts that Wells was involved, but Joe still remains critical of him.
At STAR Labs Wells and Stein share a drink and talk about how the accelerator changed their lives and work. Stein begins to stumble and faints. At the same time across town, Ronnie falls down but tells Caitlin that he is fine. It turns out that Wells drugged Stein. Eliing and his men arrive at Star Labs and retrieve Dr. Stein.
Iris is asked by her fellow reporter if she knows Caitlin. He shows a picture to her of Ronnie and Caitlin taken during their date at the coffee shop before it was under attack. Iris believes that something is going on and compares a picture of the “fire guy” to Ronnie.
Back at STAR Labs, Wells lies to the group that he was subdued and that Eliing took Stein. The only way they can find Stein is to use connection that he has to Ronnie. Ronnie begins to feel cold, at the same time Stein is being held captive in a very cold room. He tells Eiling that the firestorm project was never meant to be a weapon. Eiling tells Stein his true intentions of utilizing Firestorm for military means. Stein reveals that he does not know where Ronnie is and is electrocute. Eiling tells him the last time he did this was to a Gorilla…..uh oh.
Ronnie feels the pain that Stein is feeling. Ronnie begins to cut the word “where” in his arm. Suddenly the phrase appears on Stein’s arm as a scar. Stein then tells the group where he is by using morse code. The gang discovers that he is being held in an abandoned army base. Ronnie tells Caitlin that he must save Stein, even though there is a chance that they could permanently fuse back together. He kisses Caitlin and promises to return to her.
Ronnie and The Flash speed just outside the military base. Ronnie senses his connection with Stein growing stronger. Ronnie suddenly senses that the Stein is inside and that Eiling is holding a gun to Stein’s head. The Flash races inside the base and grabs Stein and returns him safely outside of the base. Eiling’s troops roll up in a humvee and fire a specialized missile at the Flash. It turns out to be some sort of phosphorus chemical which begins to affect the Flash right away. The only way that the Flash can save himself is that he runs extremely fast in a circle, forming a funnel of sorts. He is forced to abandon the fight.
With more of Eiling’s troops closing in, Ronnie and Stein realize that they need to join together and form Firestorm. Ronnie and Stein successfully join together and begin to kick a lot of ass. Ronnie has control of his body, while Stein maintains mental capacity. Ronnie takes out a bunch of guards with the help of Stein guiding him. Unfortunately, Firestorm is caught off guard as Eiling throws yet an ION bomb at him. The bomb temporarily disables Stein and Ronnie leaving them vulnerable. Eiling prepares to shoot them but Flash knocks out Eiling. Barry’s suit is to the point of melting off his body. Both Flash and Firestorm nod to each other and say lets go him, as both take off.
The team celebrates back at STAR Labs and Ronnie successfully separates from Stein. Both Stein and Ronnie realize that they cannot stay with Eiling on their trail. They decide to leave in order to study their condition and stay one step ahead of the military/Eiling. Ronnie kisses Caitlin goodbye and promises that he will be back. Stein tells Barry that he believes in second chances, and that he will succeed. Both men merge and take off.
Later that night Cisco sits with Catilin and talk about Ronnie.Iris shows up and questions Caitlin about Ronnie. She catches one of Caitlin’s lies about Ronnie’s cover story. This leads her to believe that something suspicious is going on and agrees to work with her fellow reporter on his investigation. Iris believes that “the burning man” used to work at STAR Labs.
Joe and Barry visit his childhood home again. Barry knows that he supposed to lose, which gives him an advantage. When he faces off against the man in yellow, he won’t make the same mistake. He wants to change the past and save is Mom.
Meanwhile back at the military base, General Eiling is abducted by The Reverse Flash. He is taken down into the sewers. Wells asks just who Reverse Flash is. Wells reveals himself and suddenly Wells hears a voice in his head calling his name. He looks behind him and sees Gorilla Grodd, who grabs him and I assume murders him.
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