'Supergirl' Star Teases New Challenge for Kara

Supergirl may be getting some unexpected help in the fight to defeat Reign, but according to series star Melissa Benoist that help comes with a new, unnerving challenge.

In Monday's episode, "The Fanatical", a disciple of Thomas Coville's Cult of Rao escapes what's left of the group with a journal that may hold the key that Team Supergirl needs to save Sam (Odette Annable) from her evil alter ego, the Worldkiller Reign. While that sounds like a huge help, Benoist told Entertainment Weekly's Spoiler Room that when she finds out what they cult is worshipping now it becomes a frightening situation.

"What she's going to face is unnerving for her," Benoist said. "She saw the way that they believed in her when they were worshiping Supergirl, but I think the train goes a little off the rails in this one, and it's out of control, and now they're worshiping Worldkillers, so it's pretty sinister."

How did the Cult of Rao go from worshipping the Girl of Steel to worshipping Worldkillers? When Reign attacks a prison intent on killing the inmates and guards, the Worldkiller comes across an incarcerated Coville. He's later seen in Reign's Fortress of Sanctuary as an ally as, with Reign's previous defeat of Supergirl, a prophecy that Reign would bring about the "end of days" had begun. It seems from Benoist's quote that that translated to the cult shifting their faith.

That sinister turn is set to be just the latest difficulty for Supergirl when it comes to the Sam/Reign situation. Benoist previously told Entertainment Weekly that the entire situation with Reign -- including the realization that her best friend Lena Luthor (Katie McGrath) has been lying to her -- is full of heartbreak for Supergirl.

"The Sam and Reign conundrum encompasses a lot of heartbreak for Kara," Benoist said. "First of all, she finds out in a way that she realizes Lena's been lying and using methods that Kara's not happy about. Also, seeing a good friend of hers that she knows is a good person deep down is a million times more heartbreaking than it was to deal with Julia. Kara's seen Worldkillers, she knows that you're able to save them, but I'm sure the heartbreak is devastating because she knows what it's going to take get through to Sam."

Fortunately, Supergirl won't have to deal with this new cult threat alone. Last episode it was revealed that Mon-El (Chris Wood) decided to stay behind in the present to help fight rather than go back to the 31st century with his wife Imra (Amy Jackson).

Supergirl airs Mondays at 8/7c on The CW. "The Fanatical" airs May 21.