NOVA investigates the theories of von Daniken and others that the Earth has been visited by intelligent beings from outer space. Among claims examined are: that the building techniques used in the Great Pyramid of Cheops are so advanced that only an extraterrestrial intelligence could have built it; and that the engraved stones of Palenque in Mexico depict an ancient astronaut at the controls of a space rocket.

In the summer of 1977 Paul MacCready, a California scientist and businessman, won the coveted Kremer Prize. His achievement was to design and build an airplane which completed, unaided, a one-mile figure-eight course entirely under the power provided by the pilot himself. This is the story of those many failures and MacCready's success.