- "No, I'm a genius. My guy's on a whole other level. His neurons are firing at super speed. Synaptic connections are off the charts. The quantum computers can't even keep up processing his results."
"The artificial Speed Force."
"The artificial fracking Speed Force. It didn't just give you your old powers back, it gave you a new one. Enhanced cognition by way of a Speed Force booster shot! [...] Barry can think fast now."
- —Cisco Ramon and Barry Allen
"The Speed of Thought" is the second episode of the seventh season of , and the one-hundred-thirty-fifth episode overall. It aired on March 9, 2021.
|When Barry suddenly gains the power of speed thinking, he attempts to use his new gift to save Iris. While Barry is thrilled with his new power, Cisco is hesitant to trust it. Meanwhile, Eva must face a shattering truth.|
Cisco Ramon has returned from Atlantis to join Team Flash as they retire Nash's fanny pack to the "Hall of Fallen Friends" that has been made in S.T.A.R. Lab. After the service, Allegra Garcia mourns Nash by staring at his picture with Maya and talking to Cecile Horton.
The Artificial Speed Force causes Barry to be able to think in super speed; he is able to calculate and foresee scenarios and their outcome before they occur and can pick which potential timeline he wishes to happen. Barry and Cisco realize they do not need Ramsey Rosso's blood to free their friends from the other dimension; they can absorb the necessary particles from Eva McCulloch herself. Allegra reveals that she has seen a note Iris wrote within the mirrorverse so they know where Iris will be and when.
Eva continues her campaign to destroy Black Hole and all weapons that were created from her research. The Flash and Cisco go to a warehouse that Eva is raiding; to assist them, Barry called Frost. During the battle, Frost is injured because Barry refuses to help. However, when the three get back to the laboratory, Barry knows the exact solution necessary to save Frost's life. When asked about his choices, Barry reveals that he calculated the most logical, not emotional, outcome that will help their ultimate cause.
Eva goes on television to promote herself as the head of McCulloch Technologies when Barry exposes for all to see that she is a mirror clone of the real Eva McCulloch. The others cannot believe what Barry has done; once again, he says that it was the most logical action needed to make Eva fallible to their assault. Barry calculates that only two options are available, the freedom of Iris or the freedom of David and Kamilla; there are not enough particles for all three. Barry mentally weighs his options and makes a logical decision.
In the mirrorverse, David meets with Kamilla and Iris, but falls violently ill. Iris realizes that those who were hit with energy from the mirror gun become sick. Kamilla falls, as well. Iris tries to assist them.
Cisco, Frost, and Allegra learn that Barry has lost his emotions. They confront him. The discussion becomes a battle where Frost takes Velocity X, becomes a speedster, and uses both her speed and her cryokinesis to stop him. Ultimately, Barry wins, because he already calculated this timeline and its outcome. He causes his friends to fall unconscious.
Barry forces Iris from the mirrorverse into Earth-Prime against her will; though she resisted, Barry did not care because he calculated that he needs Iris to fight Eva. Iris then has a seizure.
Barry's emotions return as he realizes that he has hurt everyone, because he cannot process emotions in his calculations; he has no love for anyone. In anger, he destroys the Artificial Speed Force machine.
Elsewhere, Harrison Wells is alive.
Eva decides that she is tired of being an outsider in this dimension and begins dragging people into the mirrorverse with Officer Daisy Korber as one of her first hostages.
- Grant Gustin as Barry Allen/The Flash
- Candice Patton as Iris West-Allen
- Danielle Panabaker as Frost
- Carlos Valdes as Cisco Ramon
- Danielle Nicolet as Defense Attorney Cecile Horton
- Kayla Compton as Allegra Garcia and Maya (photo)
- Brandon McKnight (credit only)
- Efrat Dor as Eva McCulloch and Dr. Eva McCulloch
- Tom Cavanagh as Dr. Harrison Wells and Professor Eobard Thawne
- Jesse L. Martin as Captain Joe West
- Patrick Sabongui as Chief David Singh
- Victoria Park as Kamilla Hwang
- Natalie Sharp as Millie Rawlins/Sunshine
- This is the first episode of the series to not feature Brandon McKnight (Chester P. Runk) after being promoted to a series regular.
- S.T.A.R. Labs has a hall for mementos of fallen allies.
- Eva completely snaps in this episode, coming up with an insane new plan.
- Harrison Wells is shown being revived at some point after Thawne killed him, though it's currently unknown when.
- This is Matt Letscher's first appearance in the Arrowverse since 2017, albeit through archive footage.
- Earth-1 Wells appears in the montage at the beginning of the episode despite having never interacted with Team Flash. This is possibly foreshadowing for his return at the end of the episode.
- When Barry explains his reasoning for making Eva unstable, he references the statistic the fandom has noted about the Big Bads; when they are stalled by emotional breakdowns, Team Flash has the greatest chance to win.
- All of Barry's choices while he operates solely on logic are the right ones, which he would have ignored if emotional. A callback to all the times he's given his enemies the lead by letting compassion get the better of him and set him back at the cost of more lives before victory. He acted in similar manner to Clifford DeVoe after gaining enhance intelligence. It is worth noting that in that state, Clifford DeVoe also displayed a similar weakness of not being able to predict emotion.
- Frost is the second non-speedster to use one of the Velocity serums, Velocity X. The first non-speedster to use one of the serums was Trajectory.
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