Teddy is a 12-year-old boy who lives at FunJungle, where his parents work. Having grown up in the Congo, he is deeply knowledgeable about wildlife and struggles with boredom in his new theme park environment. He is resourceful and driven by a strong sense of environmental ethics, leading him to investigate the park mascot's unexpected death.

Summer is the 13-year-old daughter of FunJungle's billionaire owner, whose childhood wish to go on a safari inspired the park's creation. She is privileged and frequently flanked by bodyguards, whom she creatively evades by wearing head-to-toe pink and swapping clothes with other girls. Despite her fame, she is inquisitive and sincerely cares about animals.

J. J. McCracken is the wealthy owner of FunJungle and a shrewd businessman with numerous enterprises. Though he claims to have built the park for conservation and his daughter's enjoyment, his primary motivation is profit. He is physically unassuming but wields immense power, relying heavily on marketing to draw tourists.

Martin is the highly stressed director of operations at FunJungle. He is perpetually overworked, seems close to a heart attack, and notably hates animals despite his job. He insists on wearing a three-piece suit in the sweltering Texas heat and frequently scolds Teddy, making him an early suspect due to his demands for a cover-up.

Buck is FunJungle's chief of security and a childhood friend of J. J. McCracken. A proud Texan, he dresses in a park uniform accented with a cowboy hat, bolo tie, and boots, and he carries a Bowie knife. He speaks with a slow drawl and presents himself as an affable good old boy, though his primary role is managing the park's chaotic security issues.

Doc is the highly skilled but perpetually irritable head veterinarian at FunJungle. He genuinely cares about the animals in his charge and is deeply disturbed by the rising death toll at the park. Though gruff and unwelcoming toward Teddy's snooping, his initial autopsy of Henry provides the central clue that the hippo was murdered.

Mrs. Fitzroy is an award-winning field biologist specializing in gorillas who now works at FunJungle. Having raised Teddy in the Congo, she instills a deep respect for wildlife in him. She is supportive and patient, though she initially attributes Henry's death to generalized human carelessness rather than targeted murder.

Mr. Fitzroy is a globe-trotting wildlife photographer who lives with his family at FunJungle. He is dedicated to environmental ethics and his family, willingly dropping a high-profile assignment abroad to rush home when he realizes his wife and son are in danger.

Pete is the vain head of public relations for FunJungle. His primary concern is mitigating bad press and protecting the park's bottom line. He is quick to suggest blaming radical animal rights groups for the park's problems rather than looking for real solutions.

Marge is a stern security guard at FunJungle. She harbors a grudge against Teddy for his pranks and frequently attempts to catch him breaking the rules. Despite her tough demeanor, she is considered by some to lack the intelligence needed to orchestrate complex crimes.

Charlie is a former circus clown who now poses for photographs with zoo guests. Because Henry the Hippo bit him during his circus days, costing him his job, he becomes an early person of interest in Teddy and Summer's investigation.

Henry (originally named Brutus) is FunJungle's famously ill-tempered mascot. Selected purely because his merchandise sold well, the notoriously aggressive hippo had a history of attacking keepers and clowns. His unexpected death in the park's early days sets off Teddy's investigation.

Hildegard is the only remaining hippo at FunJungle following Henry's death. She is fiercely protective of her territory and poses a significant danger to anyone who sneaks into the pools.