Elmer is an independent nine-year-old boy who lives with his mother. Outraged by the cruelty he sees at home and hears about abroad, he runs away to Wild Island to save a captive baby dragon. He packs a knapsack with common objects like chewing gum, toothpaste, and rubber bands, which prove incredibly useful in the dense jungle. He approaches dangerous wild animals with polite manners and sharp problem-solving skills.

The alley cat is a well-traveled stray who recently visited the remote Wild Island. She shares critical intelligence about the island's geography and its enslaved dragon. She advises Elmer on exactly what supplies to pack and creates a distraction so he can board a ship unnoticed.

The baby dragon is a magical creature with a single small horn, gold-colored wings, and a blue and yellow striped tail. He fell onto a riverbank on Wild Island and injured a wing. The local animals exploit his condition by tying him to a crank-operated rope and forcing him to ferry passengers across the water.

Two rigid, soldierly wild pigs who serve as the island's self-appointed security force. They spot inconsistencies in the jungle environment and immediately deduce that a trespasser has arrived. They organize a thorough search to track down the intruder and maintain their strict social order.

Mouse is a small sentry on Wild Island with large eyes and long whiskers. He suffers from a habit of switching the first letters of his words when he speaks excitedly. He serves as an early warning system for the larger animals.

Seven green-eyed, sharp-toothed felines who block passage through the thickest part of the jungle. They initially intend to eat Elmer because no explorer has ever left the island alive. Their greed for rare treats outweighs their desire for a meal.

Rhinoceros is a massive beast who guards his private weeping pool. He suffers from poor self-image because his horn, once brilliant white, has grown dingy with age. He lashes out angrily at anyone who disturbs his sorrow.

Lion is a fierce jungle cat who acts on impulse and regrets it later. He tangles his mane while picking blackberries and panics about what his strict mother will say. He plans to eat Elmer out of pure frustration over his messy appearance.

Gorilla is an enormous, fierce enforcer who manages the river crossing. He physically punishes the baby dragon for disobedience and intends to violently interrogate Elmer. A severe flea problem distracts him from carrying out his threats.

Rosie, Rhoda, Rachel, Ruthie, Ruby, and Roberta are six small monkeys living near the river. Gorilla bosses them around and forces them to search for his fleas. They struggle to complete the task until Elmer hands them a useful tool.

A group of seventeen moody, untrustworthy reptiles who populate the island's main waterway. They do not participate in the dragon's enslavement but pose a constant physical threat to anyone near the water. They possess a major sweet tooth.

Elmer's mother is a strict woman living in the city. She refuses to feed stray animals and physically punishes her son when she catches him hiding the cat. Her harshness provides Elmer with the final push he needs to leave home.

The unnamed child of Elmer Elevator recounts the story of Wild Island. They know the exact number of tangerines Elmer ate and the exact supplies he packed. They speak with absolute certainty about the talking animals and magical events of their father's youth.

The elegant mother of Lion arrives on the island for a visit via the dragon ferry. She maintains high standards for grooming and controls her son's allowance, making her an intimidating figure even to a fierce predator.

Two slow-moving reptiles who encounter Elmer at night. Because they cannot see clearly, they blindly accept Elmer's affirmative answers and assume he is a local monkey carrying a sick grandmother.