A rainy day causes Phineas and Ferb to cancel today's activities. To pass the time, Grandpa Reg tells the story about one of Ferb's Victorian ancestors, Ferbgor, who helped a scientist, Dr. Phineastein, creating a platypus monster. While locked in his own building, Doofenshmirtz tells Agent P the story about his ancestor, Jekyll Doofenshmirtz, who made a concoction brewed to turn him into a monster.