“The Fanatical” is episode nineteen of season three of Supergirl.
Lena is explaining to Supergirl, Mon-El and Winn how she hopes to rewrite Reign’s DNA. It doesn’t work and Reign is threatening her when Lena shuts her behind a reflective scatter field that hurts Kryptonians when they look at it. Supergirl complains because Lena was going to tell her about any new weapons. Lena is snippy and says it isn’t a weapon.
Kara heads to see James and gives him a confusing explanation about him telling Lena about him going to the lab for Supergirl. James says he likes Lena and has to be honest. Kara can’t be. Then the woman who stole something from Colville’s followers in the previous episode, “Shelter From the Storm”, arrives at James’s office; she has Tomas Colville’s journal and she thinks his followers are using it to make a bomb.
The woman, Tanya, explains she taught linguistics and semiotics and when Reign came the followers made her translate it as she was the only one able to read Kryptonian. And it was like a recipe for an explosive. Colville has vanished Tanya gives the address that she ran away from.
Alex is trying to convince Ruby to do something. Anything. It doesn’t work.
Supergirl and Mon-El arrive at the cult’s address; he suggests she explain to Lena as Supergirl why she did what she did. They find ash that looks to be from a person. And similar to what happens when someone is too close to a nuclear strike.
Olivia arrives at CatCo to say Tanya isn’t safe. Then she and Colville’s followers take her. James follows as Guardian and takes out their car and a couple of followers before he’s shot in the head breaking his helmet. When the cops show up, they try and arrest him and he uses a smoke bomb to get him and Tanya away. She’s impressed to find out he’s Guardian.
Alex speaks to J’onn as she doesn’t know how to reach Ruby. J’onn is having similar problems with his father, and has been reading how 3D video games might reverse his decline. Alex suggests they go to an arcade.
Winn says they need to go back to the DEO to analyse the ash; Supergirl stays to talk to Lena. Who says they were never friends, just working together and her friends know Lena wouldn’t become friends with someone who broke her trust. Awkward.
Supergirl arrives back at James’s office to find out about Olivia, who was the first to turn on Colville. She explains they found evidence that someone might have died; Tanya recognises the necklace fished from the ash. Then James gets a message. Colville’s followers will post a video outing him as Guardian unless Tanya and the journal are handed over.
The trip to the arcade does not go so well as J’onn didn’t think things through. And what the cultists are building is both dangerous and potentially helpful.