Cassie Hobbes, 17, ~5'4" (163 cm), is a teenage Natural who works with the FBI’s secret Naturals program. She is observant, compassionate, curious, stubborn, and determined, though she can also be guarded and insecure because of her past. Cassie has a strong moral compass and genuinely wants to help people, even when cases become deeply personal. Her Natural ability is profiling. She can study a person’s behavior, appearance, words, and tiny details to build an extremely accurate picture of who they are, often recognizing things they try to hide. Her ability becomes especially strong after her mother, Carly, is murdered by a serial killer when Cassie is young. She becomes determined to understand people and criminals, hoping she can eventually identify her mother’s killer. She later joins the Naturals program alongside Dean, Michael, Lia, and Sloane. Cassie is empathetic toward victims and often feels responsible for helping them. Her growing connection with Dean becomes especially complicated because of their shared experiences with serial killers.

Dean Redding, 17, ~6'2" (188 cm), is a Natural profiler in the FBI’s program. He is quiet, guarded, intense, sarcastic, and often intimidating or distant. Beneath that exterior, he is deeply loyal, protective, compassionate, and much more vulnerable than he lets people see. Dean keeps others at arm’s length because he is terrified of hurting them and constantly fears that he will become like his father. His Natural ability is profiling, like Cassie’s. Dean’s father, Daniel Redding, is an infamous serial killer, and Dean grows up unknowingly living near the place where his father commits his murders. After Daniel is caught, Dean becomes involved with the FBI and uses his understanding of his father’s mindset to help profile other killers. His past leaves him carrying enormous guilt and constantly being forced to confront the fear that he inherited something dangerous from his father. When Dean believes he has done something wrong or deserves punishment, he tends to isolate himself and deliberately put himself through uncomfortable situations rather than accept comfort from others. Despite everything, Dean is determined to prove that his father does not define who he becomes.

Michael Townsend, 17, ~5'10" (178 cm), is a Natural whose ability is emotion reading. He is cocky, playful, sarcastic, flirtatious, and constantly pushes people's buttons. He enjoys getting reactions from others and often uses humor to hide how deeply he understands emotions. Michael grows up with a wealthy father who is abusive, while his mother is absent from his life. His ability develops as a way to constantly monitor his father's emotions and anticipate what might happen next. He becomes exceptionally good at detecting fear, anger, tension, affection, and other emotional shifts. Michael also develops a habit of deliberately provoking people. If someone is going to hurt him, he'd rather push them until they show that side of themselves than be caught off guard. It gives him a sense of control over something he couldn't control growing up. Despite his reckless attitude, Michael is deeply loyal and protective of the other Naturals, and underneath the jokes, he is much more vulnerable than he lets anyone see.

Sloane Tavish, 17, ~5'6" (168 cm), is a Natural with an extraordinary ability to recognize and calculate patterns, particularly through mathematics and statistics. She is blunt, analytical, highly intelligent, and extremely literal, often saying exactly what she thinks without realizing how her words affect people. Sloane struggles to understand human behavior and social cues, which makes her seem detached or awkward even though she cares deeply about the people around her. Her parents reinforce her insecurity by convincing her that 86.5% of the time, she says or does something wrong because she doesn't understand humans the way everyone else does. She develops a habit of stealing, partly because she finds it interesting and partly because she struggles with the usual social boundaries surrounding ownership. Before joining the Naturals, Sloane spends time in Las Vegas counting cards, using her exceptional mathematical ability to identify patterns and calculate probabilities. She is fiercely loyal to the other Naturals, even when she has difficulty expressing affection in conventional ways.

Lia Zhang, 17, ~5'7" (170 cm), is a Natural with lie detection. She is confident, sharp, witty, independent, and intensely observant. Lia is skilled at manipulating conversations, using charm, sarcasm, and carefully chosen words to get what she wants. She rarely shows vulnerability and prefers to stay in control. Little is known about Lia’s childhood. Somehow, she ends up on the streets, where she quickly learns that trusting the wrong person can be dangerous. Her parents teach her to lie and recognize lies, but surviving on the streets makes those skills much sharper. She becomes exceptionally good at noticing inconsistencies, changes in tone, body language, and other signs that someone is lying. She also learns to recognize danger, including the difference between someone who has a knife and someone who doesn’t. Her independence makes her difficult to intimidate, but underneath her confidence is someone who has learned never to depend on anyone.