In "Supergirl" season 2 episode 21, Kara (Melissa Benoist) will have to make a difficult decision, so she will have to rely on someone to guide her through it and make sure she will make the right choice. With the season coming to an end pretty soon, Kara will have to overcome several hurdles.

Next week's episode will have the president (Lynda Carter) ordering Kara to do something about Rhea (Teri Hatcher) and her plan to destroy the planet. Kara will be left unsure whether or not she should follow the president's orders. Luckily, Cat(Calista Flockhart) will be making a comeback to the National City, and she will be able to guide Kara and make sure she's making the best decision for those involved in the situation.

The trailer for next week's episode starts with Cat's voice. She makes an announcement to the public, saying, "Good evening, National City. I've been away for a while, but I'm back."

Before Cat appears in the promo, it shows a scene of Lillian (Brenda Strong) walking in on Kara and her friends, which will prompt them to raise their weapons. Lillian doesn't appear to cause any trouble. Instead, she wants to have a partnership against Rhea and her army. All of this happens as Rhea and her forces of Daxamites start to invade the Earth.

In another scene, Rhea appears on television to tell the public not to resist her forces. The scene will then move on to Kara and Cat talking about the dangers of National City's current situation.

A montage of fighting scenes is shown in the trailer, which ends with a confrontation between Kara and Rhea. Rhea is heard telling Kara, "It is over, for you, Supergirl."

Don't miss out on what happens on "Supergirl" season 2 episode 21, titled "Resist," on Monday, May 15, at 8 p.m. EDT on The CW.