The Flash
Dr. Wells (Tom Cavanaugh) returns to S.T.A.R. Labs via Earth 2 in episode 5 of "The Flash" Season 2. The CW

Barry Allen (Grant Gustin) has come up against some pretty dangerous foes on "The Flash," but his biggest challenge yet may be burying the hatchet with the man who killed his mother -- well, an alternate universe version of the man who killed his mother anyway. In a sneak-peek video for episode 5 of the CW series second season, "The Darkness and the Light," Barry and Joe (Jesse Martin) are having a hard time wrapping their heads around the fact that Dr. Wells (Tom Cavanaugh) -- Earth 2 Dr. Wells -- is back at S.T.A.R. Labs.

Oddly enough, it is Barry who is more willing to trust Wells. Perhaps, that is because the scientist saved the Flash from King Shark in episode 4.

"This is a lot take in, but that guy is not Wells," Barry tells his cop father figure in the teaser video. "Eddie [Rick Cosnett] erased that Wells from existence. This guy is someone else."

That is not to say that Barry is without worry.

"You think this is easy for me," Barry asks. "The guy in there looks, moves, sounds, exactly like the guy that drove a knife through my mother's heart. I'm trying to get passed this."

Joe is not having an easy time either. Apparently, he tried to shoot the new Wells!

Watch the episode 5 sneak-peek video below:

The promo for the episode seems to confirm that the new Wells is an ally, even if he is not the friendliest version of the genius scientist.

"I'm guessing you didn't travel across dimensions just to meet the Flash," says Barry.

"That's exactly what I did," Wells responds. He wants to help Barry stop Zoom (Tony Todd). "Zoom has infected my world, and now he has come for yours."

Wells also has some important information to share about the feared bad guy. "I created him," he confesses.

Watch the promo for episode 5 below:

Will Wells help Barry stop Zoom? Fans will have to wait to find out. "The Flash" airs Tuesdays at 8 p.m. EST on the CW.