A girl, Tonya, approaches Kara and James with Coville's journal. She tells them it's basically a recipe for explosives and that Coville has vanished.
Alex tries to cheer up Ruby, but she just wants to be left alone.
Kara and Mon-El check out the place Tonya ran away from, and another girl attacks James and Tonya at CatCo. They take Tonya, but James goes after them as Guardian. His mask comes off mid-fight, but the two escape.
Alex and J'onn commiserate on not being able to get Ruby and M'yrnn out of the house. They decide to take them to an arcade.
Mon-El and Kara found evidence of the bomb Coville's followers were trying to build and give it to Winn for further research.
James gets a threat that if they don't turn over Tanya, a video of him as Guardian will be posted online.
M'yrnn has a PTSD moment at the arcade.
Supergirl and Lena figure out that Olivia and the other followers are using a rock to make a new Worldkiller. They realize they can use it as the reverse and turn Reign back into Sam.
James announces that he's going to hold a press conference and reveal he is Guardian. He's worried about how people will react when they learn Guardian is black. Tonya tells him that she wants to confront them, so he doesn't have to reveal himself.
Tonya turns herself over, and Mon-El goes with her undercover. The DEO loses the tracking signal on the van.
Kara hears Mon-El and tracks them down. She fights Olivia and tries to talk her down. It works, and they manage to get the rock out of her hand.
The rock is discharged, but Winn discovers another one in space. Kara and Mon-El take J'onn's ship to go get it. They are running out of time though, as Reign is becoming immune to Kryptonite.