Max is a fourteen-year-old scout who observes the social dynamics of Troop 52 from the middle of the pack. He avoids direct conflict but constantly pays attention to his peers, stepping in to diffuse arguments or protect his friends. He is quietly analytical and possesses a youthful elasticity of mind that helps him process frightening situations without panicking. When an unusual illness strikes the camp, his calm demeanor leads Dr. Riggs to select him as a medical assistant.

Dr. Tim Riggs is a general practitioner in North Point who serves as the town's primary physician. A man in his forties with no children of his own, he fulfills a fatherly role for the five adolescent boys in Boy Scout Troop 52. He is intelligent, responsible, and a careful planner who takes his medical and leadership duties seriously. When an unexpected stranger arrives on Falstaff Island, Tim relies on his medical training to attempt a diagnosis, though his tendency to overthink problems complicates his response to the crisis.

Kent is a physically imposing fourteen-year-old scout who acts as the unofficial leader of the boys when Dr. Riggs is absent. He enjoys asserting his authority over the other scouts, pushing boundaries, and testing his limits against adult rules. He greatly admires his father, the local police chief, and tries to emulate his decisive demeanor. This effort frequently translates into bullying and recklessness.

Newton is a highly intelligent and rational member of Troop 52. The other boys tease him for his weight and label him a nerd, but he provides valuable practical skills to the group, such as mapping trails, building campfires, and identifying local flora. He maintains a calm disposition and a thick skin, absorbing the emotional outbursts of his peers. He operates a fake online social media persona to experience positive attention free from physical judgment.

Ephraim is an impulsive fourteen-year-old scout who struggles with sudden bursts of anger. He seeks out adrenaline and takes physical risks that often lead to injuries and fights. He attends therapy to manage his volatile emotions, fearing he might end up in the legal system like his absent father. He relies heavily on his best friend, Max, to help him navigate tense social situations and calm his temper before he acts destructively.

Shelley is a quiet, inexpressive scout who deliberately draws little attention to himself. He maintains average grades at school to avoid scrutiny from adults and peers alike. Beneath his vacant exterior, he is highly observant and views other living creatures purely as subjects for his dark curiosity. He secretly tortures small animals to study their physical responses, lacking any moral qualms or empathy for the suffering of others.

Dr. Edgerton is an ambitious scientist operating a funded research laboratory. Allegedly working on a fast-acting diet pill, he bioengineers an aggressive, highly adaptable parasitic tapeworm. He conducts brutal experiments on animal and human subjects without regard for their suffering, prioritizing scientific discovery over medical ethics and public safety.

Tom is an extraordinarily thin, sickly man who stumbles onto Falstaff Island seeking food. He is a desperate, malnourished escapee from a scientific laboratory, harboring a dangerous bioengineered parasite. Despite his terrifying physical deterioration and unnatural hunger, he retains fragments of his humanity and fears the harm his condition might cause the unsuspecting boys.

Nathan is a recent doctoral graduate who accepts a job working in Dr. Edgerton's laboratory out of financial necessity. He assists in the observation of infected animal subjects and grows increasingly disturbed by the horrific results of the bioengineered parasites his employer creates.

Jeff Jenks, known locally as Big Jeff, is the police chief of North Point. He is an authoritative man who teaches his son that true leadership requires picking a course of action and sticking to it with absolute conviction, regardless of the consequences.

Reginald Kirkwood is the town coroner in North Point. He is a practical professional who occasionally allows his son to observe or assist with his medical work, inadvertently giving Max early exposure to clinical procedures that prove useful on the island.

Stonewall Brewer is an admiral in the Canadian Navy. He is responsible for enacting the strict military quarantine protocols around Falstaff Island, prioritizing rigid containment procedures over the immediate safety of the civilians trapped within the designated zone.

Claude Lafleur is a locksmith stationed at the same Navy base as Admiral Brewer. His specialized skills are utilized in classified operations connected to the laboratory from which the sick stranger escapes.

Lance Corporal Frank Ellis is a soldier stationed at the military perimeter surrounding Falstaff Island. He is tasked with enforcing the military's strict barrier and following orders regarding specific trigger words to maintain the quarantine zone.