Last season, viewers witnessed Barry Allen's first in-depth encounter with the powerful extra-dimensional energy known as the Speed Force. On tonight's episode of "The Flash," Barry will once again venture into the Speed Force, but this time, it won't be quite as kind to him as before.

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While speaking with Entertainment Weekly, "Flash" star Grant Gustin shared some insight on why fans should expect him to face choppy waters when he enters the Speed Force again. "The Speed Force takes a little bit more of an aggressive approach with Barry just because of choices that have been made since the end of season 2 leading up to where we’re at now," Gustin said. "They use different characters that will get under Barry’s skin in a different way, but also they’re just not quite as understanding anymore because of how many decisions Barry has made that have affected time and affected the timeline. So it’s a pretty different Speed Force experience than last year."

Barry's extra-dimensional excursion comes after the dramatic conclusion to last week's episode, which saw Keiynan Lonsdale's Wally West, AKA Kid Flash, trapped in the Speed Force by Savitar. However, according to executive producer Andrew Kreisberg, Barry might not just be rescuing Wally - he might be replacing him. "Barry was so busy trying to save Iris he didn’t realize it was Wally he should have been protecting," Kreisberg told EW. "That’s going to lead Barry to risk everything to go into the Speed Force to get him back, but someone always has to be trapped in the Speed Force prison. So the question in that episode becomes: Is Barry going to sacrifice himself for Wally, and how are they going to get Wally out?"

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Gustin also elaborated on Kreisberg's comments. "He’s willing to make the ultimate sacrifice when he enters the Speed Force," Gustin said of his character. "Barry is willing and wants to stay and replace Wally in the Speed Force forever. He thinks it’s what he deserves, to spend the rest of eternity in the Speed Force."

Starring Grant Gustin as the Scarlet Speedster, “The Flash” airs Tuesdays at 8 pm ET/PT on The CW. The series also stars Jesse L. Martin, Tom Cavanagh, Carlos Valdes, Candice Patton, Danielle Panabaker, Keiynan Lonsdale, and more.