Jack is a young peasant boy enduring poverty with his mother. Their desperate situation compels him to trade their sole cow for magic beans, which his frustrated mother discards. Overnight, the beans sprout into a colossal beanstalk ascending into the clouds. Driven by curiosity and adventure, Jack climbs it, discovering a sky kingdom ruled by the evil sorceress Hecuba and her son, Prince Tulip. This realm contains an enchanted castle imprisoning Princess Margaret under a powerful spell, betrothed against her will to Tulip.

Jack's initial motivations of self-preservation and exploration shift to a rescue mission after meeting Princess Margaret. He gains aid from his loyal dog, Crosby, and enchanted mice—formerly the castle's courtiers. These allies provide crucial guidance and support, demonstrating Jack's reliance on teamwork within the magical environment. His primary goals become securing the goose that lays golden eggs, obtaining a magical harp, and freeing Princess Margaret.

Jack confronts significant challenges: evading the child-eating sorceress Hecuba, depicted as an exceptionally frightening witch, and outwitting her monstrous son, Prince Tulip. The perilous castle environment features eerie sequences like paper wedding guests singing unsettling songs such as "Are You Happy?", creating psychological tension. Jack's resilience is tested, demanding quick thinking and bravery against the oppressive forces governing the cloud kingdom.

His development transitions from naive farm boy to active liberator. He directly confronts Hecuba in a climactic battle, utilizing the castle's environment and magical elements to achieve victory. Jack breaks the enchantment over Princess Margaret and the courtiers, restoring freedom to the cloud kingdom. Securing the goose ensures long-term financial stability for himself and his mother upon his return home.