When Fry destroys the Professor's precious Leonardo Da Vinci beard, he discovers a map leading to the inventor's greatest invention. The gang looks at an old copy of The Last Supper and using a super powered x-ray, discover one of the apostles was a robot and Planet Express heads to Rome to investigate.
The gang soon meets the robot, Animatronio, who leads them to Da Vinci's famed workshop where Fry and the Professor accidentally combined all the devices to create a spaceship that seneds them to Da Vinci's planet, where the inventor is still alive.
It turns out Da Vinci was an alien, and actually the dumbest of his species and came to Earth where he could feel smart, but soon got sick of being too smart. In the end he unveils his greatest invention... a Doomsday device he wants to use to get revenge on everyone that called him stupid. The Professor, who felt humiliated by also being dumb on that planet, encouraged Da Vinci, while Fry ends up stopping the machine.