"Mio, My Son" starts by introducing Bo Vilhelm Olsson ("Mio"), a young boy who has been adopted by an elderly couple who dislike boys. They harass him, and tell him to stay out of their way. One day he receives an apple from the kindly shopkeeper, Mrs. Lundin, who asks him to mail a postcard for her. He mails the postcard, but not before he has thrown a glance at it. It is addressed to a king, and it says that his son will soon be coming home, recognized by his possession of a golden apple. Bosse looks at his apple and suddenly it turns into gold.