Barry Allen (Grant Gustin) came face to face with the last person he ever expected to see again in episode 4 of the CW's "The Flash" Season 2. The return of Dr. Wells (Tom Cavanaugh) was a shock, most of all because Wells saved the superhero from King Shark. This is the man who killed Barry's mother and is responsible for much of the trauma that has plagued the Flash this season. Can Barry bury the hatchet and learn to trust Earth 2's Wells? Fans will find out in episode 5, "The Darkness and the Light."

According to the synopsis for the new episode, Barry and the S.T.A.R. Labs team have another enemy to contend with as well. It seems a meta-human called Dr. Light slips through the portal from Earth 2 and Barry needs some help from Jay Garrick (Teddy Sears) to take her down. But during a fight with the Flash, Dr. Light blinds him and drops some shocking news about Zoom (Tony Todd).

In the promo for the episode, Barry is more concerned with Wells, who arrives as 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. "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," says Wells.

Meanwhile, the synopsis also reveals that Barry asks Patty (Shantel VanSanten) out on a date. After watching the pair flirt for two episodes, viewers will be glad to see Barry finally make a move.

Watch the promo for episode 5 below:

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