On a field trip to the Natural History Museum, Paul Cooper, a boarding-school student, strays from his group and is found by the headmaster, Mr. Douglas, staring at a statue of Bigfoot. Paul insists he met the creature last summer during a vacation with his father, Will Cooper, a park ranger, who told him about a Bigfoot who likes Coca-Cola and even gave him a radio that plays rock music.
Meanwhile, Sheriff presides over the park and rallies people to hunt a mysterious large animal that mauled a deer. He enlists the help of Will Cooper and his Indian friend Jim.
That night, Paul sees a flashing purple light in his dorm window and spots Bigfoot in a cloud of purple smoke. Bigfoot tells Paul that his father is in danger and asks him to come to the park. Paul shows an agate amulet that Bigfoot gave him and asks a classmate to join; Mr. Douglas bursts in, questions him about what happened, and warns he could be expelled for telling lies.
Paul runs away and hitches a ride to the park, where he reunites with his father. They walk through the park and meet Jim. They return to Will’s cabin to find a strange man eating meat and a brood of baby raccoons that Will has adopted, all devouring the food in the kitchen. The stranger introduces himself as Morgan Hicks, a big-game hunter the sheriff hired to hunt the large animal. Paul has a nightmare in which Morgan shoots Bigfoot, and he begins to distrust Morgan.
The foursome heads into the park to hunt the animal and stumble upon a ruined area filled with crushed Coke cans. Paul’s Bigfoot amulet glows orange, and Will discovers a radio playing rock music—the same signs Paul claimed to have left there last summer. The group exits the ruins with Bigfoot watching from a distance. They later search for a sick bird and take it to the park’s veterinarian, Dr. Helen Foster, who tends to animals in an outdoor enclosure.
After dinner, they learn a door to the cougar enclosure was torn open and the cougar is gone, which fuels the hunt further. A Bengal tiger has escaped from the circus and is roaming the park, complicating their pursuit. The four track the tiger to a rocky pass, and Will tells Jim to take Paul back to school because the hunt has become too dangerous. Paul resists and continues toward the lake, where they meet an Indian elder named Red Hawk, who has a pet eagle. Jim insists Red Hawk died years ago, but Red Hawk reveals that Bigfoot saved him and shows Paul that he also bears an amulet from Bigfoot.
Red Hawk urges Paul to tell Bigfoot to retreat to the mountains, or Morgan will kill him. Jim leaves Paul with Helen while he rejoins the hunt; however, Helen agrees to take Paul along to rescue Will after Paul explains what he has witnessed about Bigfoot. As they ascend into the mountains, their truck runs out of gas, the tiger ambushes them and smashes the windows, and Morgan arrives to join the pursuit. The tiger is driven off, and the chase culminates in an abandoned mining town within the park.
They trace the tiger to the town’s tunnels, where Will is tranquilized. Paul climbs toward the ruins where Bigfoot resides and urges him to run for the mountains; a tunnel collapse ensues, trapping Will under a pile of rocks. Paul pleads with Bigfoot to come to their aid, and the creature saves him by pulling the rocks away. Morgan spots Bigfoot and pursues him, dragging Paul into a chase that ends at the lake.
Morgan follows Bigfoot to the lake, but Red Hawk appears, and his amulet glows orange, temporarily blinding Morgan. The elder’s pet eagle claws Morgan’s eyes, blinding him permanently, and he staggers into the lake and disappears.
Back at camp, they share a quiet meal and reunite the baby raccoons with their mother, who carries them back into the wild. Paul returns to school to hand in his final exam, and Mr. Douglas reveals that he received a letter from Will confirming that Bigfoot was real and that Paul’s story was true. He admits that he loves fairy tales but believed he couldn’t believe in them as an adult, and he asks if there’s a way to see Bigfoot himself. Paul explains that Bigfoot can be seen by adults only if they believe, and as the amulet glows orange again, the two of them glimpse Bigfoot in a cloud of purple smoke.
