January 2025, Newport, New Hampshire, the disappearance of Edward Walton, the son of a wealthy family, seems to be connected to the activity of a sect whose aims are secret. A team of three detectives interrogate a series of witnesses with the intention of reconstructing the past activity of the sect. Focal points of the investigations remain a room painted in white, and a suspicious sound of beating metal coming from that room, located in the house from which Edward disappeared.
Jim, a real estate agent, is the first to be questioned by Marcus, head of the team of three detectives. He says he visited the house three years earlier, when the previous owner lived there. We see what happened through Jim’s eyes, in a flashback: He hears a metallic noise coming from a room that the workers are repainting in white. He also talks to the old owner of the house: Her name is Norah, but Jim talks to this old woman calling her “Rose”. The narration comes back to the present. Brenda and David, the other two detectives listening to the interview, are captured by the detail of the white paint. This confession from Jim turns out to be just a vision, since the old woman that welcomed him wasn’t Rose, but Norah, the actual old owner of the Walton mansion.
Jim is in a diner with his boss Alice. Alice begins to suspect that the disappearance of Edward and that of Norah Thompson are connected. The cops try in vain to find clues under the paint of the room Jim talked about. The white paint put on by the old owner has gone. It has been replaced by the scarlet paint with which Hector Walton, Edward’s father, repainted the room during the renovation of the house.
Marcus tells David to contact the workers who renovated the Walton mansion. Jim goes home and confesses to Alice that he doesn't feel like sitting idle. He is the only one who has seen the house before it was renovated, and knows many of the people involved in the investigation. He suspects that a secret organization is threatening the city.
Diana, Edward’s sister, walks alone into the woods, wearing a black cassock. She meets another person wearing her same cassock (It’s Rose, we don’t see her face). Rose gives her a pendant on which is engraved the name of Diana’s mother, Judie.
Brenda goes to Claremont police station, that is very close to Newport. We find out that when she worked in Claremont, she arrested a man who was suspected to be the white room killer. Subsequently, there were other murders on full moon nights, so it was thought that the real white room killer was not him.
The detectives go talk to the workers. One of them claims to have seen the walls of the room in the Walton mansion covered in blood. The other workers deny having had that vision. On the way back, the car driven by Marcus is forced to stop. On the road appears Diana. She passes out on the street. At the hospital, Diana claims she infiltrated the cult to try to find her brother. Jim and Alice go into the woods to follow the sect that is migrating to the city.
Brenda returns to Newport police station and opens the investigation file on the lights of Newport. The lights in the archive go out suddenly, and then they come back showing blood dripping on the walls. There is a flashback, which unreliable narrator is David, that takes us back to the evening when Edward was persuaded to join the sect by killing one of the guests. Edward hasn’t actually killed anyone. David tells this story just to make the sect look evil in the eyes of his fellow police officers, Brenda and Marcus.
The station is invaded by the lights of Newport. We find out that the organization was founded by Norah Thompson, who turns out to be Edward and Diana’s grandmother from mother’s side. The aim of the organization is that of defending its members. They reunite to stay all together in a safe space, protected from the white room killer that attempts his murders on full moon nights.
Edward and Diana’s mother, Judie, had been murdered by the white room killer. Eventually, David is accused by the lights of Newport to be the killer and is captured, even if he tells Jim that he has never killed anyone. At the very end, we find out that both Jim, David, and Judie had been trapped in a white room by the old Rose when they were young. That’s why they are afraid of the white color of the walls.