Dr. Wren Muller is a forensic pathologist currently on medical leave in New Orleans. Formerly known as Emily during medical school, she survived a kidnapping by Jeremy Rose and changed her name to represent her survival. She relies heavily on routine to manage her ongoing psychological stress. Despite being officially off duty, her drive for justice pulls her back into analyzing Jeremy's new series of violence.

Jeremy Rose, known to law enforcement as the Bayou Butcher, is a serial killer currently evading the New Orleans Police Department. Having previously attended medical school under the alias Cal, he uses anatomical knowledge to harm his victims. He harbors a fixation on Wren after she escaped him years ago. He travels to Massachusetts to set a trap in the town where he spent his childhood summers.

Philip Trudeau is the pastor at Covenant of Grace Church in the Berkshire region of Massachusetts. As the son of a former judge, he has lived his entire life insulated by local power structures. He spent his teenage summers with Jeremy Rose, and the two share a hidden history involving a fatal car accident in 2002. He worries that Jeremy's return will destroy the respectable life he has built.

Richard is Wren's optimistic husband. He accepts every part of Wren's history, including the shame she feels over her past interactions with Jeremy before knowing his true nature. When Wren decides to travel to Massachusetts to consult on the investigation, Richard accompanies her to offer stability and protection.

John Leroux is a detective with the New Orleans Police Department. He took over the Bayou Butcher case from his father and feels a personal responsibility to stop the killer. Still recovering from a leg wound sustained in a previous confrontation with Jeremy, Leroux travels to Massachusetts to continue the hunt.

Corinne is a college friend of Wren who now works for the Salem Police Department in Massachusetts. Recognizing the ligature marks on a recent murder victim, she reaches out to Wren for her forensic expertise, inadvertently pulling Wren north.

Charlie is a young woman living in Massachusetts who accepts a drink from Jeremy, unaware of his true identity. She possesses a risk-taking nature that Jeremy exploits, convincing her to explore the abandoned local fairgrounds late at night.

Jenna is an animated, twenty-five-year-old partygoer in Massachusetts. When she steps away from the gathering to use the woods, Jeremy intercepts her, introducing himself under a false name before luring her onto a stolen boat.

Tom is a young, dark-haired man whose physical appearance bears a passing resemblance to Jeremy's new disguise. Driven by a sense of charity, he offers Jeremy a ride in his truck, quickly growing uneasy as Jeremy begins discussing the dangers of picking up hitchhikers.

Dr. Roy is Wren's therapist. She helps Wren process the extreme dissociation and trauma resulting from her encounters with Jeremy, reassuring her that setbacks in healing are a normal response to extreme stress rather than a complete failure of progress.

Andrew is Detective John Leroux's husband. With a bubbly and lighthearted personality, he provides a stark contrast to the grim reality of the murder investigations, offering both Leroux and Wren a much-needed mental break.

Sergeant Brixton is an officer in the small-town Massachusetts police department handling the new wave of murders. He is highly protective of his jurisdiction and reluctant to narrow his suspect list to Jeremy Rose, preferring to believe local theories about Satanic cults rather than listening to outside experts.

Morgan Davies is a young woman from Jeremy and Philip's past in Massachusetts. Following a night of underage drinking, she was struck by Philip's Jeep on a dark road. The handling of her accident forms the foundation of the dark secret that binds Jeremy and Philip together.

Kathryn is the ex-wife of Philip Trudeau. Their marriage dissolved acrimoniously, and she uses social media to post thinly veiled allegations of his infidelity, though she finds herself socially silenced by his powerful position in their church and community.