A satellite lands on Earth in the USA. The US Government is convinced this strange satellite came from somewhere that is undetectable from Earth.
They conclude that the only place that would fit that description is the other side of the sun.

Two astronauts, Larry Bets and Lewis Pearson, are enticed to check this probability out. They find another world the same size of Earth that is inhabited by a race of Gods who have a plan for the future of Earth, with a replacement race they nurtured, and do not want to be detected at this time. The Gods sabotage their spaceship to prevent Lewis and Larry's return to Earth.

There is also a person already there, of Nazi parents from 1945, that is an additional challenge of their return to Earth, because he wants to go with them.

They are joined by Terri and Bobby Bauer, two astronauts from Earth, who have a life threatening problem in their trip to the planet to rescue Lewis and Larry, and then have to convince the Gods for their return to Earth.