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.

David, Kristen and Ben assess whether a pregnant woman is possessed when she claims one of the twins she’s carrying is evil. Their investigation leads to a fertility clinic where they discover a connection to all of their encounters throughout the season. Also, Kristen questions one of her daughters’ capacity for evil upon realizing that she also used that fertility clinic.

After the shooting of an unarmed woman, the team is tasked with investigating the police officer who pulled the trigger.

Kristen, David, and Ben are sent to Cornell University, at the request of Bishop Marx, to investigate an electrode-based experiment.