Supergirl’s powers are tested when Reactron, one of Superman’s formidable enemies, arrives in National City and targets the young hero. Also, Cat plans to run an exposé on Supergirl.

Kara’s friends must find a way to save her life when a parasitic alien attaches itself to her and traps her in a dream world where her family is alive and her home planet was never destroyed. Also, Alex, Hank and the DEO must fend off a Kryptonian attack while Kara is out of commission.

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.

Eliza throws Alex and Maggie a wedding shower, which causes Maggie to reach out to her estranged father. Supergirl joins J’onn on a personal mission.

Kara makes a major life decision. Meanwhile, J'onn finds out that special DEO-caliber guns have hit the streets of National City.