Phineas Flynn and his stepbrother, Ferb Fletcher, are determined to make every day of their summer vacation fun. They try building a full-scale roller coaster, becoming musicians, building a backyard beach, and traveling back in time to meet dinosaurs. Their family pet, Perry the Platypus, doubles as a secret agent and battles evil. Meanwhile, older sister Candace is tattling on them to Mom and Dad, though she can never seem to catch them in the act.