Forensic psychologist Kristen Bouchard is hired by the Catholic Church to determine whether a serial killer is possessed by a demon or merely a psychopath.

Leland assists convicted serial killer Orson Leroux with having his conviction overturned; Kristen is called into court to testify while her daughter, Laura, undergoes emergency heart surgery; David witnesses a woman's evil instincts firsthand.

Kristen, David, and Ben face the horrors of the internet as they investigate a Slender Man-style meme that scares teens into committing blasphemous acts in order to avoid death. Leland trains Sheryl in the fine art of online trolling.