In Supergirl S03E06: Midvale, Back to Midvale High School, Alex & Kara have a mutual friend, she is murdered by her teacher, after effort on killing them failed, the teacher was arrested. But they also found out that someone who is drug dealer in accusing for killing their’s friend.
Supergirl S03E05, Kara and Sam investigate, discovering that all the affected children attended a public pool laced with a chemical which causes the same symptoms, and the manufacturer is owned by Morgan.
Maggie has recently moved out on her own and has started a relationship with Kim . However, Maggie’s mother Lila and brother, who are forced to move into her loft sublet with her, are unaware that she is a lesbian.