Kara must find a way to free her friends when Non and Indigo use mind control to turn National City’s citizens into their own army.

Supergirl is forced to do battle with an unexpected foe and must risk everything – including her life – to prevent Non and Indigo from destroying every person on the planet.

When Kara and Alex investigate the murder of an unregistered alien, the trail leads to an alien fight club run by Roulette, the ringmaster who commands aliens to fight in mortal combat for the entertainment of rich humans. While trying to stop the fighting, Supergirl and Martian Manhunter find themselves up against a surprising opponent. Meanwhile, Hank is thrilled to have found another Martian and tries to get to know M'Gann better. Supergirl takes Mon-El under her wing and begins to train him.