WARNING: This article contains major spoilers for "Pay the Piper," the latest episode of The Flash.
The key to saving Iris West-Allen from the Mirrorverse lies roughly 20,000 leagues under the sea.
In "Pay the Piper," the latest episode of The Flash, Cisco Ramon found a way to rescue Iris and the others trapped in the Mirrorverse with a little help from Hartley Rathaway, aka Pied Piper. He just needs to make a little trip to Atlantis first.
"I have an idea," Cisco said. "A way to get our people out of the Mirrorverse. We need a lossless, self-sustaining source of perpetual energy."
"Sounds like you're talking about the Holy Grail of science: a perpetual-motion machine," Harrison "Nash" Wells scoffed.
"That's right," Cisco confirmed with a grin. "Hartley had some ideas. I think we can actually build one. We're just missing one component and, thanks to my travels, I know exactly where to find it: Atlantis."
"Finally, Crisis pays off in a good way for once," Ralph sighed.
"I know time is crucial, but don't worry. I'll hurry back," Cisco added.
This won't be Cisco's first trip to Atlantis. In "Death of the Speed Force," he returned from a fact-finding mission, wherein he charted all the differences "Crisis on Infinite Earths" made to Earth-Prime. In that episode, he announced that he came back early to "wash the Atlantean fish smell off of these clothes," which indicated that not only does Atlantis exist on Earth-Prime now, but that it can be visited by terrestrial humans as well.
At the time of writing, it is unclear what that means for The Flash Season 6 finale. It is unlikely the series will actually show Atlantis this season, despite Cisco's familiarity with the location. However, it could mean that Cisco will be absent from next week's episode, seeing as he will need to travel thousands of miles to get there.
However, it may already be too late for Iris. In "Pay the Piper," she began to show signs of what Eva McCulloch calls "neural dissonance." That is to say, she is beginning to scratch her arm the same way Eva does, and she is experiencing debilitating headaches. Due to the length of time she has spent there, the Mirrorverse is beginning to change Iris, and not for the better.
In an interview with CBR, showrunner Eric Wallace teased the lasting impact the Mirrorverse will have on Iris. "When is Iris going to get out of the Mirrorverse? And how is she going to get out? And what happens when she does?" he mused. "Because the consequences of watching all of the things that she's been forced to watch is going to leave a big emotional toll on Iris. So, when she does get out, is she the same? That's the question."
Airing Tuesdays at 8 p.m. ET/PT on The CW, The Flash stars Grant Gustin, Candice Patton, Carlos Valdes, Danielle Panabaker, Tom Cavanagh, Jesse L. Martin, Danielle Nicolet and Hartley Sawyer.