'Supergirl' Season 3 Episode 10 Spoilers: Alex Labors to Keep Kara Alive

Facebook/TheCWSupergirlPromotional photo for "Supergirl" season 3.

Alex (Chyler Leigh) will not let her sister, Kara (Melissa Benoist), die in the upcoming episode of "Supergirl."

In the episode titled "Legion of Super-Heroes," the promo shows the elder Danvers doing her best to bring back Kara. Previously, her sister was defeated by Reign (Odette Annable) in the epic battle between the two powerhouses. The others could not believe that the Girl of Steel came out as the loser in the fight. This was a first for Kara, as she usually comes out victorious in her many encounters with vindictive villains.

Reign, however, is not the usual antihero. She is part of the feared World Killers, a dangerous assassin who was living as a normal human named Samantha. When the transformation occurred, nobody could have expected how powerful she was. In a recent interview, Benoist hinted what was set to happen between Kara and Reign. According to her, Reign was someone who would be difficult to take down.

"I think Reign is going to surprise people. She is pretty spectacular to behold and she definitely will give Supergirl the fight of her life. I think what sets her aside from the villains that we've seen — the Big Bads that we've seen up to this point on the show — she has a really surprising back story that's quite grounded, that gets you really invested in who she really is fundamentally," Benoist said.

The upcoming episode is expected to reveal Kara's fate. The promo does not offer many details, only that Alex will move heaven and earth to save her sister. Elsewhere, Reign is making her presence known. Now that Supergirl is out of the picture, she will show the Earthlings exactly what they will be dealing with from then on. In the clip, she is seen arriving at Kara's workplace.

"Supergirl" season 3 will return on Monday, Jan. 15, at 8 p.m. EST on The CW.