|"Things were looking a little grim, but part of me was, admittedly, a little excited for a "reunion" of old friends."|
- "There is a difference, Barry, between having powers and having precision."
- —Oliver Queen to Barry Allen
The episode acted as the first of a two-part crossover, , between and , along with the eighth episode of 's third season, "".
Barry is thrilled when Oliver, Felicity and Diggle come to Central City to investigate a case involving a deadly boomerang. Excited about teaming up with his friend, Barry asks Oliver if he’d like to help him stop Roy Bivolo, the meta-human Barry is currently tracking. Bivolo causes people to lose control of their emotions and has been using that skill to rob banks. Unfortunately, the superhero partnership doesn’t go as smoothly as Barry expected. When Oliver tells Barry he still has a lot to learn, Barry sets out to prove him wrong by attempting to stop Bivolo alone. However, when Bivolo infects Barry and sets him on a rage rampage, everyone is in danger, and the only one who can stop him is the Arrow. Meanwhile, Iris is furious when Eddie tries to get a task force to stop The Flash. Joe and Dr. Wells agree The Arrow is a bad influence on Barry and Caitlin and Cisco deal with a new team in S.T.A.R. Labs.
Barry goes to stop a bank robbery, but is too late to catch the robber. However, he notices that the people in the bank are for some reason, extremely aggressive with each other for a few minutes. During a meeting, Eddie mentions catching The Flash due to him being a number 2 LIL at the crime scene, thinking his intentions getting around is suspicious, though this was rejected by the captain. After talking with them, he took the captain's food before heading to S.T.A.R. Labs. Caitlin also gave some advice to Barry about involving Iris whether as the Flash or as Barry.
The police department is able to find the robber via tracer that was hidden in the money. When the police find the robber in a warehouse, one of the officers looks at the robber straight in the eye, causing the officer to become aggressive, and starts attacking the other officers. Barry, as Flash, goes to save the other officers, but hits the floor while saving Joe. Before the aggressive officer can shoot at Joe and Flash, the Arrow shoots the officer down to prevent him from shooting. The Arrow then compliments Flash on his mask before leaving.
At an old warehouse on the outskirts of Central City, Barry and Oliver meet up with Felicity and Diggle. While Diggle is in shock of Barry's speed even throwing his fries in the air, Felicity and Oliver reveal that they are in Central City trying to track down someone who uses razor-sharp boomerangs. Diggle states that he had a cousin who got struck by lightning once, but only developed a stutter. Barry suggests that they team up, but Oliver declines. Barry then takes Felicity to S.T.A.R. Labs, where Felicity works with Cisco to run tests on a boomerang that Oliver recovered. Diggle exclaims to Oliver about freaking out on Flash's speed which he just walks away. At S.T.A.R. Labs, Joe and Dr. Wells talk to Barry about how they don't trust the Arrow, but Barry does trust him and tells them they don't even know him.
The next day, Iris talks to Eddie about the Flash, who Eddie believes should not be out on the streets. At Iris' coffee shop, Oliver and Felicity meet Barry, where Oliver reveals that he found out the bank robber's name: Roy Bivolo. Iris appears giving Felicity and Oliver their coffee, she drags Barry away in private and expresses her amazement and excitement that he knows Oliver Queen. After being persuaded by Felicity, Oliver reluctantly teams up with Barry, believing that Barry only thinks he wants Oliver's help.
At the police station, Joe reveals that the Arrow showed up again last night, and Eddie tries to convince Singh to create a task force to take down the Flash. Singh turns him down, and Iris is hurt when she finds out that Eddie is against the Flash.
Later that day, Barry goes to the warehouse to train with Oliver, who tells him that when he goes into the field, he should be wary of his surroundings. He demonstrates this by shooting an arrow at Barry, who catches it before it can hit him, but gets shot in the back by two automatic crossbows.
At S.T.A.R. Labs, Felicity talks to Caitlin about a theory that different colored lights can change people's emotions, like red causing rage. They think of this because people who turned aggressive claim that before they started acting, they saw some red light. Later, Felicity talks to Dr. Wells, who asks Felicity if she can let him know who the Arrow is, so he can trust the Arrow more, Felicity refuses, saying that it is not her secret to tell. Dr. Wells accepts this, saying he will try and find out using other means.
Barry then comes some time later to S.T.A.R. Labs, and finds out where Bivolo is hiding. Against Felicity's advice, Barry goes in alone to Bivolo's hideout, where Bivolo uses his powers to use make Barry aggressive, and uses it to escape.
Back at S.T.A.R. Labs, Barry is checked by Caitlin, and claims he saw red before Bivolo escaped, yet doesn't feel aggressive. Before Barry leaves, he angrily complains to Caitlin about her constant nagging. He then goes to the warehouse where Oliver is waiting, and Barry starts on a rant against Oliver, and says he doesn't want his help anymore. Barry then goes to the police department, where Eddie is still trying to convince Singh about a task force against the Flash. Barry then starts raging towards Singh and Joe when confronted about the Bivolo case.
That night, an enraged jealous Barry, as Flash, goes to find Eddie, and is about to attack him. Joe goes to S.T.A.R. Labs, and tell the gang that Barry's eyes were glowing red, and he's raging. They decide they need to stop Barry fast, and ask Felicity to call Oliver Queen, revealing that Wells has found out that he's the Arrow, and in the process revealed Oliver's secret identity to the rest of the Flash team. Before Flash can hurt Eddie, he is pulled away by the Arrow, causing Barry to fight Oliver. As Flash and Arrow are fighting, Cisco, Diggle, and Caitlin argue who would win the fight. Oliver is eventually able to restrain Barry, allowing Joe and Dr. Wells to use a device of flashing multicolored lights to stop Barry's rage. Barry apologizes to Oliver for the things he said earlier, Oliver changes the subject and reminds Barry that they still have to catch Bivolo.
Off-camera, Bivolo is caught and placed in a particle-accelerator chamber. Oliver then explains to the Flash team why he chose to keep his identity a secret from them. Later that night, Flash goes to apologize to Iris about attacking Eddie, but believing that Eddie was right all along about him being dangerous, says to him to never contact her again. The next day, Felicity and Oliver go to the coffee shop, saying they are going back and want some coffees for the road. While Felicity and Iris get the coffees, Barry again apologizes to Oliver for the things he said in the field and reveals that he had feelings bottled up inside, but he just never realized it before. Oliver accepts his apology and assures Barry that he can always talk to him about anything, he also gives Barry advice about Iris to let her go, saying that guys like them never get the girl. Before leaving the coffee shop, Oliver sees Samantha Clayton, an old girlfriend of his. The girlfriend later talks on the phone with someone, and says she's picking a hot chocolate for them. Before hanging up, she says, "Mommy will be home soon", implying it may be Oliver's child from the episode "".
Elsewhere, a homeless person on the street seems to be shivering, and is about to be mugged by two guys. One of them asks if he's cold. The homeless man then gets up, releasing fire from his hands, saying he is not cold at all.
- When The Flash runs by the painter to finish his job for him, there was a sign for Palmer Technologies.
- When The Flash is talking with Iris, she asks what his name is and Barry responds with "Like Ralph or something?". This is a reference to the original 1978 Superman movie, in which a similar line is used during Superman's interview with Lois Lane.
- According to Oliver, this episode takes place one month after "".
- When Oliver comments on Barry's silly names for villains, Barry counters with Oliver's foes, Deathstroke and The Huntress. However, Oliver wasn't the one to name either; Deathstroke was a codename used by A.R.G.U.S. and The Huntress was coined by Quentin Lance.
- Whenever someone's eyes glowed red after being affected by Rainbow Raider, it caused them to be angry.
- In the DC comics, red is the color for rage on the emotional spectrum.
- The eyes that glowed red somewhat resembled the eyes of Professor Zoom in comics and most media.
- When Barry fights Eddie in his rage-induced state, he expresses anger on how the latter just "takes whatever he wants." This is similar in a reverse way as to how, in the DC comics, Cobalt Blue (Barry's long lost twin, Malcolm Thawne) views Barry's life.
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