Two women in Lewiston, Maine, were killed after being stabbed multiple times within a week. Then a man is stabbed, and killed, followed by the murder of his wife. The unsub was casing the houses before attacking. All the houses the victims lived in were supposedly haunted, according to Courtney Mably, a local blogger. Piles of salt and burned sage, used to ward off spirits, are found at the latest murder scene. Garcia finds out all three houses were chronicled about by Courtney. Garcia also located seven other houses that have similar backgrounds. A 9-1-1 call comes in from one of those locations. There JJ arrests Courtney, who has blood-covered hands. She claims she was trying to help the victim, Natasha Thompson. Natasha's daughter Michelle saw the masked unsub, who she said was a woman. But she adds it wasn't Courtney. The unsub is obsessed with the paranormal. Courtney gives Rossi a list of local paranormal investigators. Garcia finds Stephanie Carter, a local professor who, with her husband Patrick, specializes in casting out demons. Stephanie, who resembles Michelle's sketch, invites Courtney to come on an investigation with her. Stephanie went off her psychiatric medications about five years ago, when she started doing paranormal investigations with Patrick. Alvez says Patrick's notes stopped a week ago. Stephanie killed Patrick a week ago but is hallucinating that he is still alive. She tells him of her plans to kill Courtney, to stop "the infection." Courtney and Stephanie struggle and Courtney stabs her with a shard of broken glass. Stephanie gets the upper hand and ties her up to a bed, but Rossi shoots Stephanie before anything happens. Courtney lost her twin sister in a car accident, and she believes in spirits because she hopes to see her sister again.