The Flash is playing a dangerous game with time in tonight's (May 19) season finale.

The stellar first season of "The Flash" concludes with Barry (Grant Gustin) faced with a huge, life-changing decision: should he travel back in time to save his mother's life? This idea, of course, is put into his head by the recently captured Reverse-Flash (Tom Cavanagh).

But there could be serious consequences for Barry and his friends if he does go back to save his mother. For starters, he may never become The Flash, which means he would never meet his STAR Labs friends Caitlin (Danielle Panabaker) and Cisco (Carlos Valdes) -- and a life without Cisco is not a life worth living. Plus, this could potentially put Caitlin in a nefarious position for season two. And then there's Barry's love interest Iris West (Candice Patton). If Barry never lived with Joe (Jesse L. Martin) and Iris, would they even best friends? Or would they be something more by now? Would Barry even exist?!

Clearly, we have a lot of questions. So we asked the cast of "The Flash" to give us the deets on the big finale at the CW Upfronts. Here's what they could -- and couldn't -- say:

According to Gustin, Barry is feeling "a little empty" after his big showdown with Harrison Wells (aka Eobard Thawne aka Reverse-Flash). "The episode opens with them facing off, Barry and Wells," Gustin told us. "Wells kind of gets into his head a little bit and sends him down the road he wanted to send him down in the finale. Barry thinks he's making decisions that he wanted to make for himself, but Wells has gotten into his head."

Barry's decision to travel back in time will also have major implications for his friends. Iris, who recently learned of Barry's superhero identity, has a lot to lose in the finale.

"The idea of time travel and traveling back in the past, we've seen a little bit of that and how it changed the course of the future," Patton told us. "What does that mean for Iris and Barry? What does that mean for Barry and Joe?"

"It could change everything as we have known it to be," she added. "That's a scary thing -- when you start playing with time."