arry Allen is a forensic scientist from Central City. After helping Arrow and his team on a case, Allen returned home. During the unveiling of S.T.A.R. Labs' particle accelerator, an explosion rocked the city and gave certain people superpowers. The explosion caused an accident and rendered Allen comatose. When he awoke, he discovered he gained super speed. He took up a costumed identity, the Flash. While frantically searching for a USB drive containing crime scene statistics, Flash was told by Cisco Ramon that his modified algorithm flagged a possible metahuman in Detroit. Believing a metahuman outside of Central City could be something more, Flash recruited Arrow to back him up in the investigation. Flash and Arrow went to Detroit in pursuit of Mari McCabe. After she took on the speed of a cheetah and ran off, Flash sped off after her annoyed by Arrow's comment she could move fast. Despite his own super speed, Flash was unable to capture McCabe.
Flash was amazed by McCabe but mistook her camouflage with teleportation. However, during the pursuit, McCabe fell off the edge of a building. Flash ran after her but was amazed to see her fly back up to the top. Once she agreed to a discussion, Flash insisted he should do the talking so he had more experience with metahumans. Arrow quickly pointed out Flash threw most of them into his pipeline prison. McCabe didn't understand what a metahuman was. Flash explained the term and its connection to the S.T.A.R. Labs incident. She denied being there so Arrow had Felicity Smoak run a check. Flash asked Arrow to tell her he said hi. Smoak heard him and greeted him back. However, he couldn't believe McCabe had powers without exposure to the dark matter explosion. Flash tried to offer her his help but she turned down and warned them to stay away from her. After she flew away, Flash was relieved the talk went well and he wasn't beat up a little like usual.
Flash and Arrow went to Chuck's house again after they learned McCabe was fighting crime in an outfit. She managed to convince them to let her figure out things on her own for awhile. Flash promised if she ever needed any help, they would answer her call. After McCabe asked for a codename, Flash blurted out Cisco Ramon kept calling her "Vixen" then denied being affiliated with anyone named Cisco. Arrow wondered if Flash and Felicity Smoak were separated at birth. Flash hoped they weren't because they kissed then realized Arrow didn't know about that. He sped off.