Griffin is an 11-year-old student known as "The Man With The Plan." Frustrated by feeling ignored by adults, he asserts himself by organizing complex, detailed operations to solve his friends' problems. He pays meticulous attention to detail but struggles when unforeseen variables disrupt his carefully constructed contingencies.

Ben is Griffin's more cautious, level-headed best friend. He manages narcolepsy, a sleep disorder that causes him to fall asleep unexpectedly, which makes him fear he is a liability to the team. Facing an impending transfer to a special boarding school, he suppresses his anxiety over danger to make his remaining time with Griffin count.

Savannah is an 11-year-old recognized as Cedarville’s greatest authority on animals. She advocates fiercely for the ethical treatment of all creatures and possesses an uncompromising dedication to their welfare. Her headstrong personality drives the group's mission, though her all-or-nothing outlook occasionally forces her friends into stressful, high-stakes situations.

Mr. Nastase is the well-dressed but cruel owner of All Aboard Animals, a paddleboat zoo where creatures live in squalid conditions. He utilizes his status as an adult to operate shady business dealings and maintain his reputation while severely neglecting the animals. His greed leads him to prioritize profit over the health and safety of the captive creatures.

Klaus is a large, burly security guard employed by Mr. Nastase at the floating zoo. Though he appears tough and intimidating, he sleeps heavily on the job and takes quick action only when directly disturbed. He views his position simply as a paycheck, remaining unaware of his employer's illegal operations early on.

Darren is an arrogant, untrustworthy classmate of Griffin and his friends. He views himself as superior to the other children and frequently tries to manipulate situations for his personal benefit. Because he has access to a boat and sailing experience, the group reluctantly recruits him, though his selfish ambitions consistently complicate their plans.

Melissa is the group's shy, introverted technology genius who prefers the company of computers over people. She frequently hides her face behind her hair but contributes immense value to the team through her expertise with surveillance and electronic systems. She provides quiet, thoughtful suggestions that balance out her more impulsive teammates.

Pitch is the athletic, outgoing climbing specialist of Griffin's crew. She brings physical capability and outdoor knowledge to the team, helping them navigate obstacles that require agility. Her tendency to jump into situations quickly and act before thinking makes her a foil to the more methodical planners in the group.

Logan is an aspiring child actor seeking his next big break after losing a commercial gig. He utilizes his talent for performance to create convincing distractions and gather intelligence for Griffin's plans. Serving as the group's comic relief, he frequently drops unrelated one-liners into serious conversations.

Cleopatra is Savannah's beloved pet monkey. Her sudden disappearance deeply upsets her owner and acts as the catalyst for the children's investigation into the All Aboard Animals paddleboat. She shares an unusually close and playful bond with Savannah's large dog.

The Ferret is one of the small animals rescued from Mr. Nastase's floating zoo. It quickly forms a strong attachment to Ben, seeking him out as a place of safety and refusing to leave his side during the day.

The Owl is a captive bird at All Aboard Animals. Mr. Nastase trains the creature to act against its natural instincts, forcing it to terrorize and attack the other captive animals to keep them too frightened to attempt an escape.

Savannah's pet dog is a large, intimidating animal that frightens the other children but remains fiercely loyal to Savannah. The dog plays a role in sniffing out clues and protecting Savannah's property from intruders.