The DEO investigates the rash of dead animals; it spreads to humans, as people develop flu-like symptoms with a large scratch on their wrists. Imra believes this is the work of Pestilence, the third Worldkiller.
With Mercy and Otis having poisoned the air with Kryptonite, Alex and Lena have Kara placed into a protective suit, which filters the Kryptonite, but means Kara can’t go out and fight as it may damage the suit and kill her.
During the meeting with Cat, Kara coincidentally uncovers that she is Superman’s cousin. After Cat uncovered the relationship, Kara is assaulted by Reactron, who looks to murder her so as to get his retribution on Superman, yet she figures out how to send him escaping.
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.