After narrowly escaping Winnie-the-Pooh and Piglet’s deadly rampage, Christopher Robin flees the Hundred Acre Wood and returns to his hometown of Ashdown, desperately seeking help. However, when the bodies of Maria and her friends are discovered in the woods, Christopher is wrongly accused of their murders.
The tragedy, soon labeled the “Hundred Acre Massacre,” spawns a film adaptation that further tarnishes Christopher’s reputation in Ashdown. Few believe his account of the events, including his childhood friends Lexy, Finn, and Aaron, his parents Alan and Daphne, and his younger sister “Bunny.” Now a social outcast, Christopher is haunted by nightmares of Pooh and seeks help from hypnotherapist Mary Darling to cope with the trauma of his twin brother Billy’s kidnapping during their birthday party years ago—a disappearance that remains unresolved.
Meanwhile, back in the Hundred Acre Wood, Pooh, Piglet, Tigger, and Owl are forced into hiding after their home is burned down. The group continues their violence by slaughtering three university students—Alice, Jamie, and Mia—in a recreational vehicle. Owl urges Pooh to bring their wrath to Ashdown rather than waiting for more victims to stumble into the woods. A group of hunters, led by Aaron, eventually ambushes the creatures and kills Piglet as revenge for the students’ deaths. In retaliation, Pooh kills the hunters but reconsiders Owl’s proposal after Aaron escapes and returns to Ashdown.
As the town turns against Christopher, he loses his job as a doctor at the local hospital and intensifies his hypnotherapy sessions with Mary. When Aaron arrives at the hospital for treatment, Christopher suspects that Pooh is responsible for the attack, which Aaron confirms. Christopher also encounters Cavendish, a hospital janitor he recognizes as the man who kidnapped Billy. In a confrontation at Cavendish’s home, the truth is revealed: Cavendish was employed by Dr. Arthur Gallup, a scientist who paid him to kidnap children in Ashdown for gruesome experiments involving animal genes. The children, including Billy, did not survive and were buried in the Hundred Acre Wood, where they transformed into half-animal, half-human hybrids with enhanced healing abilities. Overcome with guilt, Cavendish confesses to murdering Gallup before taking his own life.