Cassie is a 17-year-old profiler in the FBI's Naturals program. She possesses an innate ability to read people and figure out their motivations, a skill she developed while traveling with her con-artist mother. Following the traumatic revelation that her aunt was a serial killer, Cassie tries to find emotional balance while remaining deeply committed to stopping violent criminals. She keeps a tube of Rose Red lipstick as a physical connection to her fractured past.

Dean is a gifted profiler and the first recruit of the Naturals program. He carries the heavy burden of being the son of an infamous serial killer, causing him to harbor intense internalized anger. He hides his emotions behind a quiet exterior, fearing that he might inherit his father's violent traits.

Michael is a Natural who reads emotions effortlessly, a skill he developed to anticipate his abusive father's moods. He uses humor and spontaneity as defense mechanisms. He frequently provokes anger in others as a way to surface and manage unpredictable feelings.

Lia is a human lie detector within the Naturals program. She developed her ability to spot deception to protect herself from a traumatic past. She projects a brash exterior and manipulates situations to test people or guard her vulnerabilities.

Sloane is a brilliant statistician who processes facts and probabilities at lightning speed. She categorizes the world with mathematical precision, taking note of minute details like rope length or car models from a simple glance. She struggles with social cues and feels insecure about her differences.

Special Agent Sterling is the new evaluator and supervisor of the Naturals program. She presents an authoritative demeanor and insists the teenagers focus on their education rather than active cases. Her severe suits and rigid posture mask a painful history with the FBI.

Daniel Redding is an organized serial killer currently serving a life sentence in a maximum-security prison. He possesses unremarkable physical features but projects immense psychological dominance. He views his son as property and delights in manipulating law enforcement.

Briggs is a seasoned FBI agent who helps oversee the Naturals program. He is dedicated to solving cases and protective of the teenagers, though he frequently clashes with his ex-wife over how to manage them.

Judd is the FBI agent responsible for maintaining the house where the Naturals live. He acts as a grounded presence for the teenagers and works closely with the supervising agents to ensure the facility runs smoothly.

Emerson is a young college student whose murder acts as the catalyst for the current FBI investigation. Her death mimics the specific methods of an incarcerated serial killer, drawing the Naturals into the case.

Fogle is a criminology professor at Colonial University who teaches a popular class called "Monsters or Men: The Psychology of Serial Murder." He harbors a morbid fascination with violent criminals and previously interviewed famous killers for his research.

Geoffrey is a teaching assistant for Professor Fogle's criminology class. He displays a chilling admiration for serial killers and presents lectures on their methods with disturbing enthusiasm.

Clark is a shy, seemingly nerdy student in Professor Fogle's criminology class. He displays underlying signs of anger and rejection when discussing his murdered classmate.

Derek is a handsome, confident student who participates in the same study group as Emerson Cole. He represents one of the initial suspects the Naturals investigate at Colonial University.

Trina is a woman living in Dean's hometown who frequently visits the local maximum-security prison. She appears naïve and cruel, harboring a dark obsession with an incarcerated killer.

Christopher is Trina Simms's teenage son. He is highly aggressive and defensive, particularly regarding his mother's strange choices in romantic partners.

Webber is an overzealous guard at the maximum-security prison where Daniel Redding is held. He relishes his small amount of power over visitors and strictly enforces facility rules to assert dominance.

The Director of the FBI, he oversees major programs including the Naturals. He expects results and frequently pushes back against those who want to shield the teenagers from active fieldwork.

Lacey Locke is a former FBI agent who previously mentored the Naturals. She possesses a dark history that directly impacts Cassie's emotional state as the new investigation begins.

Lorelei is Cassie's mother, a gifted con artist who taught her daughter how to read people. She disappeared under mysterious circumstances when Cassie was twelve, leaving behind her signature Rose Red lipstick.

Marie is Dean Redding's mother. She abandoned him during his early childhood, leaving him in the custody of a violent serial killer.