Lena admits that she experimented on Sam for three weeks, and that she used Kryptonite to keep her contained. 

Sam and Julia talk to each other in the valley dimension. Kara passes out and sees them for a second too. The Worldkillers are causing a total eclipse to end the world. 

Sam and Julia are beginning to forget who they are, but they fight to remember. Grace is dead. 

Kara asks James to use Guardian to find out for sure if all of Lena's Kryptonite is gone. 

They come up with a plan to have Brainy send Kara, Lena, and Alex into the valley. Kara asks Mon-El to leave her in even if things go south. 

James is supposed to break into Lena's vault, but he can't do it. Instead he lies to Winn and says there's no Kryptonite. 

Lena, Alex, and Kara find Sam and try to help her wake up. It works, she goes back to her body, but Reign comes to the valley. 

Winn presents Alex with a new suit that he designed for her. They get the Worldkillers' location from Sam and go to fight them. Kara weakens due to the eclipse. They get through to Julia, who fights off Reign, but Pestilence attacks her. They end up killing each other and Reign absorbs their powers.  

Imra tells Mon-El that Pestilence is dead and they can go home now. 

James tells Lena that he's Guardian and admits that he broke into her lab, but didn't go into her vault because he trusts her. Lean tells James that it wasn't Lex's Kryptonite. She figured out how to make it.