Flashbacks reveal young Kara experiencing kryptonite for the first time; Nia and Brainy are trapped by invading aliens; a young Cat Grant may be the reason Supergirl never gets out of the Phantom Zone.
Nia and Brainy attempt to save Supergirl from the Phantom Zone by time travelling back to Kara's home in 2009; a young reporter named Cat Grant sets her sights on Midvale as she suspects there is a big story in the small town.