“Reign” is episode nine of season three of Supergirl and the mid-season finale.
Sam wakes from a nightmare of her flying with heat vision scorching something. Ruby comes in and talks about the trip Sam went on in “Wake Up”. Sam has no memories of anything about that.
At the DEO, Mon-El and Imra are talking about the future. And that governments were being overwhelmed by violence and chaos. They banded together as the Legion to help keep the peace. And the Legion exists because of Kara; their example to aspire towards. In the future, darkness was spreading and they went on a mission, only to go through a wormhole. They crash-landed in the past and because they travelled by accident, couldn’t get home. So, entered cryosleep to go home the long way, only for the torpedo to damage the ship and wake Mon-El up. They need to fix it to get home.
Kara is hosting a party and she and Alex talk about Mon-El and Maggie. Ruby and Sam arrive late; Lana thinks Sam looks tired. Sam thinks Lana and James are attracted to each other. As does Kara. Then J’onn says they have a call and have to go.
In a field outside the city, a symbol has been burnt. It’s Kryptonian in origin and Kara has seen the symbol before. Her mother tells her that the symbol predates recorded history and she can’t translate it.
At CatCo, James is briefing the staff on following up on the symbol. Lana wants a word in private; she thinks Morgan Edge is behind it. Both pay Edge a visit and he denies having anything to do with it. He’s telling the truth.
Kara speaks to Winn as they arrive at the bar; she’s sure someone out there knows what the symbol is. Then Mon-El and Imra call them over. Kara feels awkward and Winn takes Imra to the bar. Mon-El says his ship is broken beyond his understanding. Then Kara gets a collect call from Albatross Bay Correctional Facility.
She heads there and speaks to Thomas Colville, from “The Faithful”. He quotes something that isn’t from the Book of Rau. And that the symbol is that of World Killer. Colville, during his travels, got information predating the Book of Rau. The symbol is that of the dark god, the devil, and he met a disgraced Kryptonian priestess from Fort Rozz. This is the god before Rau. Three steps lead to the end of days. The mark of the beast, the work of the beast, which is many deaths, and finally the reign of the beast, when she comes. World Killer. To bring about the end of days. And Supergirl needs to stand against her.
Sam has been changed into Reign, but doesn’t consciously know it. She is killing, though. Kara finds seeing Mon-El and Imra together hard; not a great surprise. And Reign is a very dangerous foe.