The world is celebrating the moon landing, when an old British flag and a document claiming the moon in the name of Queen Victoria is discovered on the lunar surface. A search on earth turns up Arnold Bedford (Edward Judd), who is the last survivor of the Victorian expedition. He relates the tale of how Joseph Cavor (Lionel Jeffries) invented an anti gravity substance called 'Cavorite' and built a spacecraft in 1899. An accident at launch leads to Katherine 'Kate' Callender (Martha Hyer) accompanying Bedford and Cavor on their trip to the moon. Once they get there, they discover an ancient alien civilization that seems to be a bit too interested in mankind and earth.