Claudia's death was first mentioned in Season 1's Lunatic, and it was first suggested that he may have the same disease she had in Silverfinger. It is revealed that Claudia Stilinski died from complications due to frontotemporal dementia, which Stiles is believed to have inherited as a result of his recent symptoms, such as sleepwalking, vivid dreams during the day, and an inability to tell dreams from reality.It is also revealed that in Galvanize, the Nogitsune used William Barrow to trigger Kira's foxfire so that Stiles would be shocked by it through his baseball bat (which was found at the electric substation by Derek and Kira), thereby jump-starting the Nogitsune's power inside of him.
It is confirmed that Stiles is possessed by a Nogitsune in this episode.The Nogitsune, now in complete control of Stiles's body, confronts the remaining Oni, who are revealed to be led by Kira's mother. The power then goes out, due to the Nogitsune having damaged the wiring on the roof the previous night. Stiles has an MRI scan to test for frontotemporal dementia, the same illness that caused his mother's death. Derek and Kira find Stiles's baseball bat at the power station, and Derek deduces that Kira was indirectly responsible for the Nogitsune taking over Stiles's body. Scott's mother and father find Stiles, who had been sleepwalking. Lydia leads them to the mental health center where Barrow was committed, only to find that Stiles is not there. Stiles makes a panicked late-night phone call to Scott after he finds himself in a strange location with his leg in a steel trap. Scott and the others set off on a search.