In the comics, the 1940s version of the villain used tricks of slowness in battle against Jay Garrick (played on The Flash by Teddy Sears), while his successor, a scientific genus who went by the name Turtle Man, created devices based on slowness to battle Barry Allen (Grant Gustin). On the show, the team hunts down this meta-human who can slow time itself.

“In a surprisingly funny twist, Cisco [Carlos Valdes] has actually been hunting The Turtle the entire series,” executive producer Andrew Kreisberg says. “To Barry’s surprise, everybody knows about Cisco’s hunt for the great white whale, which is The Turtle; he’s the only one who didn’t know about it. We love the idea that there was a villain out there that they knew about, but they just haven’t bothered to tell the audience about yet. All Barry wants to do is get faster, because if he can get faster, he can take on Zoom. He’s going up against a villain who is literally slowing him down. This is one of our best episodes coming back that we’ve ever done. It feels big and emotional.”