8. Flash vs. Arrow

Roy Bivolo, a metahuman with the power to send people into an uncontrollable rage, uses his powers to rob the Central City bank. Police detective Eddie Thawne proposes to capture the Flash because he was at the crime scene, but is rejected by the captain. The police track Bivolo to a warehouse, where he uses his powers on a cop to facilitate his escape. Barry Allen arrives to save Joe West, but is almost injured himself before Oliver Queen, as the "Arrow" vigilante, arrives to stop the cop. Later, Oliver informs Barry that he and his team are in Central City tracking down intel on a killer who uses lethal steel boomerangs.

Barry and his friends suggests that they team-up to catch each other's targets and Oliver reluctantly agrees. Oliver tries to teach Barry to be more mindful of his surroundings, but Barry decides to go after Bivolo by himself. Bivolo uses his ability on Barry's mind; but because of Barry's speed, its effects last longer and he begins to snap at those he cares for.

Eddie continues to persuade his superiors to form a task force unit to capture the Flash, expressing his zero tolerance for vigilantes. When an enraged Barry, as the Flash, attacks Eddie, Oliver tries to stop Barry, and the two engage in a fight. Oliver manages to wrangle Barry long enough for Harrison Wells and Joe to use strobe light to reset Barry's emotional state. Barry and Oliver capture Bivolo and place him in the pipeline prison at S.T.A.R. Labs. Due to the incident, Eddie forms a task unit to arrest the Flash.

Barry confirms Oliver's belief that the former has still a lot to learn. Oliver advises him to stay away from Iris West, with whom Barry is in love, for a while, because men with secret identities as vigilantes never succeed romantically. Oliver asks Team Flash to keep his alter ego as the Arrow, a secret. A new mysterious metahuman able to manipulate fire appears in Central City.

In a flashback set in Hong Kong, Oliver learns how to torture suspects to gain information. In the present, Oliver and Roy Harper locate Digger Harkness, the boomerang-wielding killer, where they find A.R.G.U.S. operatives looking for him as well. Caitlin Snow and Cisco Ramon arrive in Starling City to help Felicity Smoak investigate Sara Lance 's homicidal murderer. Digger attempts to kill Lyla Michaels, Roy, and Oliver, but Barry arrives and stops him. Later, Lyla reveals that Digger was part of the Suicide Squad. When Oliver uses his extreme interrogation methods on a Russian mob member to locate Digger, Barry questions how emotionally stable Oliver is with his past tragedies to torture people.

Digger locates Oliver's base and wounds Lyla before escaping. In order to leave town, Digger plants five bombs around the city. While Oliver captures Digger, Barry uses both of their teams to defuse the bombs simultaneously. Digger is incarcerated on Lian Yu with Slade Wilson. Before Barry and his team's departure to Central City, Cisco and Caitlin gives Oliver his suit improvements and utilities, he and Oliver learned their lessons and decide to have a friendly duel.