Maggie is an 11-year-old girl living in London who struggles with a severe stutter. Her difficulty speaking isolates her from peers and causes intense anxiety in social situations, prompting her to seek comfort in a small bedroom cupboard where she cares for injured animals. To avoid being sent to a strict institution called Granville by her father, she travels to Cornwall to stay with her grandfather. In this rural setting, she discovers an affinity for the natural world and a silent connection with a large, unusual cat in the local woods.

Rumpus is a juvenile snow leopard recently separated from his sister and sold as an exotic pet at a London department store. Disoriented by his forced domesticity and subsequent release into an unfamiliar English forest, he acts more like an overgrown, awkward kitten than a fierce predator. He struggles to survive in the wild, lacking hunting skills and seeking food near human settlements, which inadvertently frightens the local villagers.

Fred is Maggie's eccentric, white-haired grandfather who works as a country doctor in Cornwall. A passionate nature enthusiast, he fills his cluttered stone cottage with natural artifacts and spends his spare time tinkering with improbable mechanical inventions. As a conscientious objector from World War I, his pacifist beliefs caused a severe rift with his son-in-law, Vincent. He provides Maggie with a warm, judgment-free environment where she feels safe.

Lord Foy is a wealthy landowner in Cornwall who holds the deed to Wildoak forest. He views the ancient woodland purely as a financial asset and makes plans to clear-cut the trees to sell the property to a copper mining company. He carries a silver-knobbed cane and actively manipulates public sentiment, spreading rumors about opponents to ensure his business ventures proceed without interference.

Evelyn is Maggie's mother, a nurturing woman who attempts to shield her daughter from her husband's harsh expectations. She pays close attention to Maggie's emotional needs and accepts her completely, stutter and all. She advocates for Maggie's trip to Cornwall as an alternative to a strict disciplinary school, demonstrating her quiet persistence in protecting her child.

Vincent is Maggie's father and a former Royal Air Force serviceman. His experiences in World War II left him with unseen emotional trauma, which manifests in a rigid need for order and control in his household. He views Maggie's stutter as a defect that needs fixing and insists on sending her to the severe Granville institution. He maintains a cold, distant demeanor and remains estranged from his father-in-law over differing views on military service.

Arabella is a fashionable London resident who receives a snow leopard as a surprise birthday gift. Though initially amused by the novelty of an exotic pet, she ignores the care instructions and leaves the animal unsecured while she attends a party. She prioritizes her own convenience and home decor over the welfare of the living creature in her care.

Nurse Nora is the medical attendant at Maggie's school in London. She lacks sympathy for Maggie's anxiety-induced injuries and views her stutter as abnormal and disruptive, recommending a harsh disciplinary facility as a solution.

Rosie is a captive juvenile snow leopard and Rumpus's sister. She shares a display enclosure with him at Harrods Department Store before they are permanently separated by a sudden purchase.

Martin is a driver employed by Arabella's brother. He delivers the large cat to Arabella's apartment and is later summoned to discreetly remove the animal after it damages her home, leaving it alone in the woods.

Brae is a local man in Cornwall who helps guard a captured animal in a farm shed. He exhibits cruelty toward the frightened creature and suggests killing it to profit from its pelt.

Nigel is a farmer in the Cornwall area. He participates in local efforts to capture the unknown predator roaming the woods and offers his agricultural property as a secure holding location.