Jeremy is a brilliant, intellectually honest Nobel Prize-winning scientist. He acts as the lead researcher and figurehead of the Wildfire Project. He is famous for both his scandalous private life and his rigorous professional genius. He demonstrates a strong dedication to the scientific mission and readily adjusts his theories when presented with new evidence.

Mark is a surgeon and the unexpected final member of the Wildfire team. He is selected primarily because his unmarried status fulfills the requirements of the "Odd Man Hypothesis." He initially treats the top-secret project with casual disregard and ignores his briefing files. His focus on the human element of medicine provides a crucial counterweight to his colleagues' strict data analysis.

Charles is an experienced and highly respected pathologist known for his messy, sloppy appearance. He prefers to let his intellect speak louder than his clothes. He functions as Jeremy's deferential counterpart during the initial town investigation, though he lacks his leader's immediate ruthlessness when making difficult field decisions.

Peter is a skilled clinical microbiologist with a pessimistic outlook. He possesses a sharp mind capable of solving complex problems even while asleep. He harbors a serious medical condition that he hides from the rest of the team, fearing professional embarrassment and marginalization during the crisis.

Arthur is the chief duty officer who receives the initial distress signals regarding the downed satellite. Tired and careful, he evaluates the crisis and makes the decision to activate the Wildfire protocol. He coordinates the early military response and reconnaissance flights over Arizona.

Peter is an elderly man living in Piedmont, Arizona, who mysteriously survives the initial biological event. He suffers from a stomach ulcer and self-medicates heavily with aspirin and alcohol. His unique physiology provides the Wildfire scientists with puzzling but vital medical data.

Jamie is an infant who, alongside Peter Jackson, survives the otherwise entirely lethal biological event in Piedmont. The child is recovered by the scientists in protective gear. The baby's survival presents a medical mystery for the Wildfire team.

Roger is a military lieutenant assigned to track and recover the downed Project Scoop satellite. He conducts the initial, fateful reconnaissance of Piedmont alongside his technician, observing unusual environmental details before entering the town.

Lewis is a military technician tasked with tracking the fallen satellite. He operates the scientific instruments in the van parked outside Piedmont, confirming the object's location before the team drives into the danger zone.

Edgar is a military monitor who oversees the tracking team's progress in Piedmont. His boring night shift is interrupted by the sudden crisis on his radio channel, forcing him to escalate the situation.

Alan is the local physician in Piedmont. He is the first person to examine and forcibly open the recovered satellite capsule, inadvertently exposing the town to the organism.

Allison is Jeremy Stone's current wife. She is left confused and annoyed when military escorts pull her husband away from a dinner party without explanation, representing the personal cost of his top-secret work.

Sam is a reconnaissance pilot. He flies a spy plane low over Piedmont to capture detailed photographs and struggles to process the horrifying sight of the deceased townspeople despite his military training.

Jaggers is the military site's top reconnaissance interpreter. He analyzes the aerial footage of Piedmont and spots the crucial movement of a survivor, changing the military's approach to the town.

Willis is an Arizona highway patrolman who briefly passed through Piedmont on the night of the incident. He later exhibits severe paranoia and violence at a local diner, expanding the scope of the crisis.

Kirke is a foppish and highly logical scientist originally chosen for the Wildfire team. Because he is hospitalized at the time of the crisis, Mark Hall is brought in to replace him on the mission.