Sam wakes up thinking it was all a bad dream. 

Mon-El reveals that he started a group in the future called the Legion. He asks if they can help fix their ship and send them home. 

Kara hosts a holiday party at her apartment. Sam and Ruby arrive and Alex bonds with Ruby. Sam and Kara tell Lena they can tell she and James are into each other.

Kara and J'onn get a call about a symbol burnt into a field. 

Lena suspects Morgan Edge has something to do with the symbols. 

Kara gets a call from Coville who tells her about World Killer and the three steps that lead to the end of days. He tells her World Killer is the third step and she's here to bring the end of time. 

James and Lena are attacked in an alley. Lena believes Edge hired the attacker. 

Members of a gang are killed by heat vision, confirming the World Killer is Kryptonian. 

Reign attacks Edge in his office, but he hid in his panic room. 

Lena offers James a drink for saving her life and they wind up making out. 

Supergirl and Reign face off in an epic battle, leaving destroyed holiday parties in their wake. Kara loses the fight and is badly injured. She's brought back to the DEO, but is unconscious and close to dying.