“Midvale” is episode six of season three of Supergirl.
Kara and Alex arrive in Midvale, as Kara had said in the previous episode, “Damage”, that they were going home, Kara driving J’onn’s ‘car.’ Eliza speaks to Alex, who then heads inside. Later, Eliza talks to Kara and Kara realises that Eliza is worried about her, too. Kara says too many people depend on her and she isn’t human; she’s realised she has to walk away from certain vulnerabilities. She’s thought about this and is happy. Eliza doesn’t think Kara seems happy.
Kara heads into their old room, where Alex is drinking. She tries to reassure Alex, who points out Kara shut down for six months. Both manage to annoy the other.
Ten years ago, and the two get up as Eliza calls them. They’re squabbling a lot and Alex isn’t happy she has to babysit for Kara later and Kara isn’t pleased about having to do human stuff. At school, Alex is good with the academic side; Kara has a physical advantage in sports. Alex does stick up for Kara at one point. At lunch, a boy, Kenny, joins Kara after being bullied by the American football team; Kara breaks the table as she watches. Kenny says he has dirt on the players and says Alex is only the way she is because she misses her father. He wants Kara to meet him in a clearing at 10 PM.
Kenny has a telescope, which in the future is on the Danvers’ porch, and he’s rigged it up to send photos to his laptop. He asks Kara if she can imagine about other worlds out there. She can. They nearly kiss. Kara sneaks back in and Alex isn’t happy. Alex had a great life and two great parents; now all she has is Kara and she’s not worth it.
As they arrive at school the next day, Kara hears sirens and then that the body of a 17-year-old male has been found. She heads there. It’s Kenny.
At school, Kara is looking at Kenny’s locker when Alex comes over. None of them knew Kenny. The quarterback makes a joke and Kara goes and confronts him; Kenny had found out he was smoking pot. Kara heads to Kenny’s parents’ house; it seems his telescope is missing. The sheriff tells Kara it’s dangerous and warns her off. Naturally, Kara starts poking around, and is joined by Alex.
Most of the episode is set in the past, and essentially shows how Kara and Alex gained a decent relationship whilst they looked into Kenny’s death.