The CW's "The Flash" has been playing around with the concept of parallel universes for the entirety of Season 2. But in episode 13, things took a major turn as the heroes went on an adventure to Earth-2 to stop their greatest villain yet. 

The first of this two-part episode began by laying out some clear rules for traveling between different versions of Earth. Barry (Grant Gustin) and Cisco (Carlos Valdes) were hard at work closing all but one of the portals that the mysterious villain Zoom has been using to travel from Earth-2 to Earth-1 to attack The Flash. Their plan is to take Harrison Wells (Tom Cavanagh) back through the last remaining wormhole and use Cisco’s newly discovered “vibing” powers to locate Zoom and his captive, Jesse Wells (Violett Beane). 

The trio race through the portal, but destabilize it in doing so. While they travel through a void of time and space (that included a nice wink to the hero’s coming “Supergirl” crossover), the machine powering the last portal back home gets destroyed. Apparently there are consequences for closing all but one, leaving Barry and Cisco stuck in the stylized “Golden Age” Earth-2.

They arrive in the parallel world and immediately find that things are very different, not just aesthetically. They bump into the doppelgangers of villains from there that are just ordinary people here, such as Henry Hewitt, Deadshot (Michael Rowe) and a very off-putting mention of a Mayor Snart. Wells cuts the sightseeing tour short to have Cisco try his vibing goggles to locate Zoom. Unfortunately, they don’t work because the frequency of Earth-2 is different from Earth-1, where they were designed. The setback means they’ll need more time to track Wells' daughter. In order to expedite the process, Barry finds his Earth-2 doppelganger, a dorky CSI technician with no superpowers. After very humanely knocking him out, the hero goes undercover as his parallel persona. 

He hopes to use the Central City Police Department resources to find Zoom, but quickly learns, despite the lack of superpowers, his Earth-2 life isn’t any less complicated. For starters, he’s married to detective Iris West (Candice Patton). Unable to resist the urge to check out his life with the doppelganger of the woman he loves, he abandons his task of finding Zoom. While checking out their house, Barry gets an emotional call from his mother, who isn’t dead on Earth-2. After he’s done crying, Iris takes him on a date to see her father, Joe West (Jesse L. Martin) the professional singer at the Jitterbug cafe. That’s right, it turns out Joe has been hiding a set of pipes from Earth-1 Barry all this time. It becomes clear early on that Joe doesn’t like Earth-2 Barry, and for good reason. Apparently Iris quit her job at the newspaper to become a detective so that she could fund Barry’s continued Ph.D. education. Now, thanks to him, Joe's daughter is on the front lines of the hunt for Zoom. 

The Flash "The Flash" Season 2, episode 13 saw the introduction of Killer Frost (Danielle Panabaker) and Deathstorm (Robbie Amell) as the gang traveled to Earth-2. Photo: the CW

Before he has a chance to digest that information, two familiar faces burst in and attack the club. Killer Frost, a meta-human doppelganger of Caitlin Snow (Danielle Panabaker) with some unique frost abilities, and Deathstorm, the doppelganger of Ronnie Raymond (Robbie Amell). Together, the sadistic couple are hunting down breaching meta-humans on behalf of Zoom. They track Barry to the club, and Detective West springs into action. She’s no match for the villainous couple and ends up in the line of fire, forcing her father to dive in front of one of Deathstorm’s blasts. Barry clears the villains from the area without anyone noticing his powers. 

Although they aren’t technically the Iris and Joe that he knows and loves, Barry feels a strange obligation to be there for them and sits by Joe’s hospital bed until he wakes up. He has just enough time to tell Iris he loves her and give her husband his reluctant approval before he dies. Just like that, the hunt for Zoom is put on the back burner as Barry and Cisco devote all their efforts to stopping Killer Frost and Deathstorm, much to Wells’ dismay. After all, his daughter’s life is hanging in the balance. 

While all this is happening, the team back on Earth-1 is having some serious trouble with a new meta-human named Geo-Mancer (Adam Stafford). Sadly, their odds of beating him are drastically diminished without Barry in town, so they turn to their new friend Jay Garrick (Teddy Sears), who was resident good-guy speedster on Earth-2. Although he lost his powers experimenting with the performance enhancer Velocity-6, Caitlin fabricates a new, less lethal, version of the drug for him to try against Geo-Mancer. Although it works for a time, the drug wears off in the middle of his fight and the villain escapes. Living to terrorize Central City another day.

Back on Earth-2, Cisco joins Iris in the hunt for her father’s killers, claiming he has developed a gun that can hurt Killer Frost. They chase the villains to an abandoned warehouse where they quickly lose the element of surprise and get captured. Just when they think they’re about to be served up to Zoom, the evil duo’s true employer enters. It turns out they work for a villain by the name of Reverb, who also happens to be Cisco’s doppelganger. Reverb seems to be in complete control of his vibing powers and tells Cisco that he is the one who answers directly to Zoom, but that could change if they combined forces and became gods. 

He pretends to think about it for a moment, buying Barry enough time to rush in and attack. He picks a fight with the three supervillains and finds himself overwhelmed by the very angry combined forces of Deathstorm and Reverb. When it looks like they’re about to kill him, Killer Frost reminds them that Zoom insisted any speedsters they encountered were to be kept alive. Almost as though she’d summoned him, Zoom shows up to agree with her statement. He kills Deathstorm and Reverb, leaving Killer Frost alive as a reward for her loyalty. 

The episode ends with Zoom snatching up Barry’s unconscious body and bringing him to the same prison that he’s been holding Jesse. The hero insists that he and her father will rescue her, but Zoom teases that it's an empty promise. The final line of the episode is a chilling declaration from the villain that Barry is standing in the last room he’ll ever see.