Supergirl does battle with the deadly Master Jailer, who is hunting and executing escaped Fort Rozz prisoners. Also, Cat hires a second assistant, Siobhan Smythe, who immediately tries to one-up Kara, and Kara and James disagree over the DEO's methods.

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 turns on her friends and the citizens of National City after being exposed to Red Kryptonite makes her malicious and dangerous. Also, Cat appears on THE TALK to discuss Supergirl.

J'onn J'onzz reveals the details of meeting Kara and Alex's father, Dr. Jeremiah Danvers, and assuming Hank Henshaw's identity. Also, Kara debates trusting someone new with her secret identity and Siobhan plots against Kara.