Forensic psychologist Kristen Bouchard is hired by the Catholic Church to work with David Acosta, a priest-in-training, and contractor Ben Shakir, to determine whether a serial killer is possessed by a demon or merely a psychopath. Kristen finds that she has a taste for the work and is invited to join the team on a permanent basis.

Kristen, David and Ben are called to investigate a supposed miracle when Naomi Clark, a 17-year-old soccer player, comes back to life after she had been declared dead for almost two hours. Kristen meets with her former boss at the Queens District Attorney's office, where she runs into Leland Townsend.

After a high-strung theater producer's behavior turns from demanding to what is believed to be demonic, Kristen, David and Ben are called in to assess the situation. Kristen discredits Townsend before he can ruin a 17-year-old boy's life.

Kristen, Ben and David are hired to evaluate Eric, a seemingly psychopathic 9-year-old boy. Eric takes a liking to David, which leaves them hopeful they can curb his violent behavior. Also, Kristen is most affected by this investigation as she worries about her young daughters who lied about a horror game their grandmother, Sheryl, bought behind her back.

On Halloween night, Kristen and David are sent to assess an exorcism, but once the pair analyzes the situation, they are at odds while trying to determine whether it is a supernatural demonic possession, or severe mental disease escalated by physical and mental distress. Also, Ben goes on his favorite show, "Demon Hunters," where he debunks their supernatural finds with fellow unbeliever Vanessa.

The Catholic Church asks Kristen, David and Ben to assess the veracity of a local prophetess, Grace Ling, and they are shaken when they see one of her visions come to life. Also, David struggles with jealousy when he sees God speaking with the prophetess, and to Kristen's dismay, her mother, Sheryl, and Leland begin a relationship.

When Bridget confesses to murder during her exorcism, Monsignor Korecki asks Kristen, David and Ben to investigate if the details match any open cases and if the woman really is possessed by a demon.

When David recognizes one of the sigils in his father Leon's artwork, he and Kristen journey to a remote art commune to investigate its meaning and how it's related to David's family.

David is shocked to learn he is being sued for inflicting severe psychological harm on Caroline Hopkins, after he assisted in her exorcism. The accusation leads him to question his future as a priest, especially once he develops a very close connection with his defense attorney, Renée Harris.

Kristen, David and Ben are called to investigate an insidiously addictive Christmas song that's spreading among an increasing number of students, and the dangerous relationship between online influencers and their impressionable young followers.

After David is badly wounded, he is determined to fight off the menacing presence of death from his hospital bed.

Leland assists Orson Leroux with having his conviction overturned. Kristen is called into court to testify while her daughter undergoes emergency heart surgery. While paying a visit to a woman in need of spiritual advice, David fears for his safety after witnessing her 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. Kristen questions one of her daughters’ capacity for evil upon realizing that she also used the same fertility clinic.