Now that the “Crisis on Earth-X” has been averted (somewhat), it’s time to refocus our concerns on the immediate dangers threatening the superheroes of The CW. Let’s begin in National City, shall we?

“I think Reign is going to surprise people,” Melissa Benoist says of Supergirl‘s fall finale (Monday, 8/7c), which finally pits the Girl of Steel against the long-gestating villain. “She’s pretty spectacular to behold, and she will give Supergirl the fight of her life. What sets her aside from the Big Bads that we’ve seen up to this point on the show [is that] she has a really surprising back story that gets you really invested in who she really is fundamentally.”

And although Benoist acknowledges that Kara’s “will always choose to fight to change someone’s mind or to make someone see the good in the world,” conversion might not be possible in this case.

“She’s the Big Bad, she’s a Big Bad, so it’s really everybody trying to figure out … what they have [to do] to be able to take her down as quickly as possible,” adds Chyler Leigh, who says there will be a “collective force coming from Supergirl’s side” to stop Reign.

Sam’s transformation will be especially difficult on Lena, who’s not only losing her company’s CFO (“I choose people badly, don’t I?” Katie McGrath jokes), but she’s also losing someone she now considers to be a close friend. “You see how close Kara, Sam and Lena are getting, I can’t imagine that it isn’t going to become difficult with Sam essentially being Supergirl’s arch-enemy and all three of us being friends,” she says. “It’s got to come to a head somehow.”

“She’s a lot stronger, I think, or will become a lot stronger than anyone expected,” adds David Harewood. “She’s full of surprises, and I think audiences are going to be … I’ll put it this way: I walked on set the other day and was shocked at what I saw. It’s a pretty arresting sight. Reign doesn’t exactly treat people with kid gloves.”

Your thoughts on Supergirl‘s Reign storyline? Drop ’em in a comment below. (Reporting by Vlada Gelman)