Kara travels to Superman’s Fortress of Solitude in hopes of learning how to defeat Indigo, a dangerous being who can transport via the Internet and who has a connection to Kara’s past. Also, James’s relationship with Lucy reaches a crossroads.

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.