Lovebirds Eloise Larkin and Arthur Royal, who are performing in an amateur theatrical production, have a dress rehearsal to attend, but Eloise must first find a baby-sitter for her siblings, a baby sister and a precocious eight-year-old brother, Donald. As no baby-sitter will watch the mischievous Donald more than once, Eloise calls Polly, a very tall person who runs an employment agency. Before going on a date with her boyfriend, the colossal Sgt. Riley, Polly sends Jack and his "agent," Mr. Dinkel, to the Larkin house. When Jack and Dinkel arrive, Donald is ready to terrorize, but instead becomes fascinated by Jack's incompetence. After permitting Jack to read aloud Jack's favorite story, Donald soon takes over when the words get too tough. As Jack slips into drowsiness, he hears this story: A muddleheaded boy named Jack lives with his mother in a village that is terrorized by a giant. The giant has stolen the royal jewels, so Princess Eloise must marry Prince Arthur from a nearby kingdom, sight unseen, for the sake of the kingdom. On her way to be married, she stops for a drink of water at Jack's house. The giant has also stolen the village's food, making times so hard that Jack's mother orders him to sell their only cow, Henry, to the butcher, Mr. Dinkelpuss. On the way, Jack meets the prince, who confides that he is unimpressed with a princess who would marry for money. As they talk, they hear the giant nearby and when the rumbling settles, Jack realizes that the prince is gone. In the village, Dinkelpuss tricks Jack into accepting five magic beans for Henry, instead of money, but then loses Henry to the giant. Meanwhile, Jack happily heads home, until he learns from the villagers that the giant stole the princess. At home, Jack tells his mother about the stolen princess and the magic beans. Resigned to Jack's stupidity, she has him plant the beans, hoping that they at least might grow into something edible. By morning the beans have become a towering beanstalk that Jack decides to climb, telling his mother that he will avenge his father's death at the hands of the giant, save the princess and find Nellie, their stolen hen who lays golden eggs. After hearing about the hen, Dinkelpuss decides to follow Jack up the beanstalk. At the top, Jack and Dinkelpuss see the castle, but on their way there, the giant catches them and takes them as prisoners. Meanwhile, in the castle, the prince and princess are locked up and overseen by the giant's giant housekeeper, Polly, and Patrick, a talking harp. As both want to be liked for themselves and not their royal status, neither informs the other of his or her true identity. However, the prince, pretending to be a troubadour, wins the heart of the princess with his singing. Jack and Dinkelpuss are put to work, but arrange for the prince and princess to meet for a moonlight stroll in the garden. Watching them, Polly and Jack are inspired to dance together. Polly, who is willing to help, Polly suggests they can escape using the trunks of skinny trees to catapult them beyond the walls of the locked garden. The next morning, Jack almost becomes the giant's breakfast, but Polly and the others knock out the giant with a log. Unable to exit through the locked door, they escape by swinging on a chandelier through a high window, out to the garden. Almost everyone, including Henry and Nellie, gets out, but Jack is delayed when the giant awakens. After a vigorous fight, Jack reunites with the others in the garden, but when it is his turn to be catapulted over the garden walls, he forgets to get on the tree and is left behind. Finally, Jack climbs the wall, but the giant follows him. The rest of the group climbs down the beanstalk, and Dinkelpuss reports Jack's heroic death to the waiting villagers. When the king arrives for the marriage ceremony, the prince and princess are both unhappy to learn that they have been deceiving each other, but soon make up. Then Jack is spotted climbing down the stalk, with the giant close behind him. On the ground, Jack grabs an ax and chops down the beanstalk, causing the giant to fall to the earth, then through it, all the way to China. As the villagers cheer, their hero kneels before the king to be crowned. Back at the Larkin household, Jack is awakened when Donald crowns him with a vase. Eloise and Arthur return from their rehearsal, and Jack, confusing the story with reality, leaves the house filled with delusions of grandeur.