- "Yeah, I may be the one in the suit doing all the running... but when I'm out there helping people, making a difference... you're all out there with me. I finally realized something: we were all struck by that lightning."
- —Barry to Team Flash
Barry escorts Iris to a university gathering honoring scientist Simon Stagg. When six gunmen storm the event, Barry changes into The Flash and tries to stop them. While he does save a man's life, he passes out before he can capture the robbers, which frustrates him. As Dr. Wells, Caitlin and Cisco scramble to find out what's wrong with Barry, Joe comes down hard on Barry for taking the law into his own hands and risking his life. Barry realizes that it wasn't six gunmen but a meta-human named Danton Black, who can make multiple copies of himself. Meanwhile, Iris becomes even more intrigued by the "red streak".
- Grant Gustin as Barry Allen/The Streak
- Candice Patton as Iris West
- Danielle Panabaker as Dr. Caitlin Snow
- Rick Cosnett as Detective Eddie Thawne
- Carlos Valdes as Cisco Ramon
- Tom Cavanagh as Dr. Harrison Wells
- Jesse L. Martin as Detective Joe West
- Patrick Sabongui as Captain David Singh
- Michael Christopher Smith as Danton Black/Multiplex
- William Sadler as Simon Stagg
- John Wesley Shipp as Dr. Henry Allen
- Michasha Armstrong as Java
- Evelyn Chew as Woman
- Emily Delahunty as Paige
- Amina Elkatib as Young Iris West
- Eli Gabay as Fire Chief
- Suzanne Ristic as Tenant
- Patrick Roccas as Prison Guard
- Ronald Patrick Thompson as Samaritan
- Seth Whittaker as Security Guard
- Logan Williams as Young Barry Allen
With help from Cisco, Barry begins using his abilities to stop minor crimes and help citizens across the city. As Barry begins to push himself more and more, he begins to develop debilitating side effects. While assisting Iris on a school assignment, Barry witnesses a robbery by a crew of men, but faints while trying to stop them. The S.T.A.R. Labs team determine that Barry is becoming hypoglycemic from the use of his abilities due to a sped-up metabolism and needs to ingest more calories to maintain his energy level. The team eventually learns that the robbers are actually one man, Danton Black, who has the ability to create clones of himself. Black wants to kill his former employer, Simon Stagg, who stole Black's cloning research. With encouragement from Joe, Barry goes after Black and successfully stops him from killing Stagg. However, Black commits suicide to prevent being captured. Afterward, Barry accepts Joe's help in finding out who really killed Barry's mother. Later, Wells visits Stagg, who has already become obsessed with the Flash after witnessing his powers and plans to exploit him as he did to Black. To protect Barry, Wells kills Stagg.
Behind the scenes
- At S.T.A.R. Labs, Cisco built a treadmill designed to handle Barry's speed. It is possibly a tongue-in-cheek reference to the Cosmic Treadmill from the original comics.
- Barry's metabolism weakness is first seen in this episode. Much like the 1990s TV series, and the comics, Barry needs to eat massive amounts of calories to replace the energy he uses while running. Failing to do so will cause dizzy spells and eventually shock from low blood sugar.
- Stagg Industries and Simon Stagg played a part in the origin of the superhero Metamorpho in the comics.
- Hex's Gun Shop is probably a reference to Jonah Hex, a hero who uses guns. Jonah Hex later appear on , another Arrowverse show.
- Alternatively, the word "hex" is the Greek word for "six", a probable reference to the plot point that six men (Multiplex and five clones) rob the store.
- At the start of the episode, the firemen who report that they're en route to the burning building respond as "ladder 52". This is likely a reference to the DC New 52 comic book line (a universe resulting from the Flashpoint story line), which is largely based on.
- This is the first full episode of the Arrowverse that doesn't include Stephen Amell as Oliver Queen at all.
- At the end, when Wells is sitting in front of Stagg, he takes off his glasses. When camera angle changes to the back of Wells, facing Stagg, Wells now has his glasses back on. When the camera changes to face Wells again, he's holding his glasses in his hand again.
- While Team Flash explains how Danton can clone himself, they never go into how Danton can clone his clothes and shoes, but not a gun.
- Cisco says that Barry will need to eat the equivalent of 850 tacos, which would be somewhere between 120,000 and 150,000 calories a day. However, in "", Barry states he needs to consume approximately 10,000 calories a day.
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