Lena provides Alex with a safehouse to protect Ruby from Reign, who is looking to severe the last ties of humanity that Sam has with her family. Meanwhile, Supergirl discovers that Lena has been manufacturing Kryptonite, and the Legionnaires depart for the future.

Supergirl and Mon-El find a remnant of Krypton drifting deep in space. Meanwhile, Alex faces a killer from her past, and Winn ends up babysitting Ruby.