Supergirl finds an opportunity to escape from the Phantom Zone but it comes with some dangerous strings attached; Lena joins the Super Friends on a mission but finds she disagrees with their plan of action.
Young Kara experiences kryptonite for the first time, Nia and Brainy are trapped by invading aliens, and a young Cat Grant may be the reason Supergirl never gets out of the Phantom Zone.
Nxyly gets hold of the Humanity Totem, causing chaos throughout National City. Meanwhile, Esme meets her new foster family and Lena attempts to cast her first spell.
Supergirl continues to fight Nyxly for the remaining totems but after Nyxly kidnaps William, Supergirl realizes she needs to take a more proactive stance to keep National City safe. Meanwhile, Alex faces the biggest challenge of her life.
Nxyly goes after the Dream Totem, and Nia must join forces with her sister Maeve to stop the imp. Meanwhile, Supergirl worries that she's being pulled in too many different directions.
When Lex Luthor appears by Nyxly's side, Supergirl and team must deal with the emotional fallout of facing their two biggest foes at the same time. Alex makes plans for the perfect proposal to Kelly, but work keeps getting in the way.
In the epic series finale, Supergirl is joined by familiar faces from the past to help her stop Lex and Nyxly for good. Meanwhile, Alex and Kelly prepare to walk down the aisle.