In the quiet darkness of a London orphanage, young Sophie peers out of her window, unable to sleep. Her life takes a fantastical turn when she spots a towering, mysterious figure prowling the streets. This figure turns out to be a 24-foot-tall giant, who whisks Sophie away to Giant Country upon realizing he's been seen. Despite initial fears, Sophie soon learns that her abductor is the Big Friendly Giant, who, unlike his fellow giants, refuses to eat children and is gentle and kindhearted. He is an outcast in his world because of his unorthodox dietary choices and his refusal to bully others.

The Giant introduces Sophie to the wonders and perils of his world, including the dream-catching and the threat posed by the other giants, who are twice as big and twice as scary, and enjoy snatching and eating human children. As Sophie and the Giant form an unlikely friendship, they decide to hatch a plan to confront the other giants and stop their man-eating ways. Their quest for justice takes them on an adventure from the cobwebbed Giant Country to the lush landscapes of Dream Country and back to the human world. Together, Sophie and her new companion set forth to seek help, aiming to create a world where dreams can thrive without the interference of the monstrous giants.