Wikipedia
A nuclear war has rendered Earth inhospitable, and only a few humans have
survived on the moon base, with no means of leaving as they lack the energy
source to power the spaceship built by Obi. One day, a small ship with a few
survivors arrive from Earth; among them hides the Moon Führer, the former
commander of the base, who reveals to Obi that he's not a human but a Vril, a
reptilian species who has arrived on Earth during the age of dinosaurs and had
accidentally triggered the evolution of primates into humans. The Vril live
below the Earth (which is hollow) and possess an infinite source of energy in
the form a cup, the Graal. Obi and a few friends fly back to Earth and enter
the world of the Vrils. They manage to steal the Graal, thereby collapsing the
Vril society, and return to the Moon, but they are followed by the Vrils'
mothership. Despite being attacked by a Vril Hitler riding a Tyrannosaurus
inside the moon base, they manage to use the Graal to power Obi's ship and fly
away. They are chased by the Moon Führer aboard the Vrils' ship, but
eventually manage to get rid of it and fly to Mars (where a Soviet mars base
awaits them).