The Martian Chronicles

S2 E11: Armek (guest star Terrell Tilford), 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 shapeshifted into M'gann and is now loose in the building, the team realize he could be disguised as any one of them.