Phineas was born into a struggling family and raised by his grumpy sister Candace. One day, he meets a mysterious old man (Grandpa Clyde), who gives him a handful of beans which he says will give him the "best day ever", but an outraged Candace stomps them into the ground. The next day, a giant beanstalk grows in Phineas' front yard, and curiously climbs up to a giant castle in the sky. Inside he meets a talking golden harp (who actually doesn't talk much), a kidnapped princess named Isabella, and a platypus who lays golden eggs, who Phineas names Perry. But Phineas' adventure is cut short when he discovers the castle is inhabited by a giant named Buford.