The Full Circle (S01E15)

The centuries roll back for the occupants of the moon through a time warp of 40,000 years to the Stone Age and meeting up with themselves as cavemen. The discovery of a planet, given the name of Retha, has a bewildering outcome when a seven-man landing party fails to return. The Eagle in which they were travelling, brought back to the moon by remote control, is found to be empty except for the body of a Stone Age man. (iTunes)