The Flash star Grant Gustin breaks down emotionless Barry, the latest Wells twist

Warning: This article contains spoilers about Tuesday's episode of The Flash.

What happens when Barry Allen (Grant Gustin) loses his humanity? Nothing good according to this week's episode of The Flash.

In Tuesday's installment, titled "The Speed of Thought," Barry gains a new ability, speed-thinking, thanks to the Artificial Speed Force. Unfortunately, the power starts overriding his emotions and humanity, and Barry starts making decisions based purely on a logic like a computer. When it comes time to choose between saving Iris (Candice Patton) or Kamilla (Victoria Park) and Singh (Patrick Sabongui)from the Mirrorverse (alas, for technological reasons they can't save all three), emotionless Barry still chooses Iris. He defeats the rest of Team Flash, all of whom try to stop him. Not only that, but Iris starts seizing after robot Barry forcefully drags her out of the Mirrorverse and leaves their friends behind. The sight of an unconscious Team Flash and injured Iris gives Barry a necessary shock to the system that wakes his emotions back up.

Below, Gustin breaks down Barry's brief dark turn and previews what's to come on the Wells and WestAllen front.

ENTERTAINMENT WEEKLY: The show continues to give you opportunities to stretch. I thought you did a good job of tracking Barry gradually losing his emotion in this episode. How did you approach playing an emotionless Barry?

GRANT GUSTIN: I was nervous, actually, about it. It was supposed to be toward the end of last season. My first day of shooting that episode was gonna be a Friday, and I think it was March 13 or 14, but that was the day we shut down.

I was nervous about starting it because it was a lot of work. I realized maybe as a crutch that I lean on as an actor, and something that I think helps me make my dialogue for me, is that I memorize it and on the day when we're working, if you fumble something or stutter on a word and it comes out in a way that feels natural (that's how people talk), I've kinda made that part of the way Barry talks. I had to get rid of all of that for this character because it was supposed to be so free flowing and robotic in a way. [Showrunner Eric Wallace] had referred to it as Spock Flash, just completely emotionless. So, there was almost this computer-like staccato rhythm to the dialogue that we had to create, which meant I had to nail it. There were big long-winded lines I had, and I had to get rid of my normal speech pattern as Barry, which was the biggest challenge. Not to mention the vernacular they gave me because the character is saying all of these big scientific, mathematical words that Barry would never usually use.

So, it was definitely a fun challenge. Like you said, I tried to build less and less emotion as the episode went. We were trying to find those checkpoints of, "Okay, here he stops using contractions." There was this progression to the dialogue. It was fun, definitely different than any other challenge I've had on the show.

Did you actually approach it like you were playing a completely different character?

Yeah, kind of. As it built for sure. In that first scene, there was that fun excitement. That was still Barry like, "Holy crap, I have speed thinking now!" And all he's thinking about is, "This is exciting and this is gonna help us get them out of the Mirrorverse." At that point, I'm still playing Barry Allen, but it develops in a way where we completely lose Barry's empathy and his normal personality and his emotions. So by the end of it, I'd like to think at least it was a completely unrecognizable character [and] you're not looking at Barry Allen anymore because the ASF has taken over his mind.

How does Barry handle the emotional fallout from his fight with the team and hurting Iris?

Yeah, it's obviously really hard on Barry. Seeing Iris lying there and the rest of the team also unconscious snaps him back to reality and the ASF leaves the body and his mind. There's an immediate emotional fallout. We pick directly up with this moment in 703, with a very emotional scene. Thankfully, Team Flash has become a family and they all have Barry's back in the wake of this and really help him feel like this wasn't his doing. He was unaware of what he was doing. His mind had been taken over. It's not his fault, but it's hard for Barry to shake that feeling that he almost killed his wife, and could've killed the entire team. So, it weighs pretty heavily on Barry. Thankfully, no one turns on him.

The real Harrions Wells returns at the end of the episode, which explains how Tom Cavanagh is still part of the show after Nash and the Council of Wells died last week. What can we expect from this version of Harrison?

Well, there's kind of a twist there, too, like always when it comes to Wells. It's not like necessarily the real Harrison Wells, I guess. It has more to do with the particles that made up all of the Wellses now embodies this Harrison Wells. So, we're going to yet again see Tom do something slightly different than we've ever seen, and it is technically the real Harrison Wells but with a twist.

Eric previously said season 7 was very much about watching Barry and Iris tackle problems together as a couple and exploring how they handle being married and heroes. After spending so much time apart in season 6, how does it feel exploring that relationship from that perspective?

It's been nice. It's definitely the next stage in their relationship. They've been married for a few years now, and we're seeing them talk about what's next for them in their life, what's next for them in their relationship, talking about having kids potentially in the future. We see Iris exploring what the fallout was for her psychologically being trapped in the Mirrorverse for all that time, which I thought was a really cool storyline for Candice [Patton] and Iris to have. We didn't see much of them together at all last year, so it's nice to have the Barry and Iris scenes back as a consistent dynamic on the show and to see them exploring what's next for them in their marriage outside of being the Flash and [on] Team Flash.

The Flash airs Tuesdays at 8 p.m. on The CW.

(Video provide by The CW)

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• Grant Gustin reveals how he learned to channel the Wellses on The Flash
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• Barry enters the Mirrorverse in The Flash season 7 trailer