Armek, a White Martian, descends on National City intent on taking M’gann back to Mars to face her punishment as a traitor. Hank and Supergirl determine the best way to keep M’gann safe is to bring her to the DEO. However, when it is revealed that Armek shape-shifted into M’gann and is now loose in the building, the team realize he could be disguised as any one of them.

Psi, a thief with psychic powers, attacks National City. Able to immobilize people by tapping into their worst fears, Psi proves a formidable opponent for Supergirl. Meanwhile, James and Lena are at an impasse, and Samantha starts her new job at L-Corp.

Colonel Haley makes a surprising decision regarding Supergirl. Kara writes a series of articles highlighting aliens in National City in the hopes that humans will stop being so fearful of them. Unfortunately, the article puts some of the aliens in harm’s way.

Supergirl, Alex, and Brainiac thwart an alien attack while William investigates Kara. J'onn J'onzz and Kelly use Obsidian tech to solve a problem.

Kara's investigation into William Dey's "criminal" activities results in the shocking revelation he is not who she thinks. Meanwhile, the conflict between Malefic and J'onn J'onzz reaches a boiling point.

Supergirl is determined to keep everyone safe from Lex and Nyxly so she doubles down on patrol, especially as Alex and Kelly's bachelorette party is coming up. Alex is torn between duty and finally allowing herself the time to enjoy her new family. Brainy receives heartbreaking news, and William clashes with Andrea over her recent coverage of Lex.