The boys are helping Ferb's grandfather live his life long dream - to jump a gorge in his motorcycle, the Holy Mackerel. Meanwhile, Perry sets out to stop Dr. Doofenshmirtz from exacting another petty revenge that dates all the way back to the sandbox.

The boys learn about one of Ferb's Victorian ancestors, who helped a scientist create a monster. Meanwhile, Doofenshmirtz recalls the story of his great-great-grandfather Dr. Jekyll Doofenshmirtz.