Two Complete Novels in One Book:
SLAVES TO THE METAL HORDE by Milton Lesser: Johnny Hope knew the robot armies had been created to serve Man. But war and a plague had destroyed civilization, leaving humans as Slaves to the Metal Horde.
THE FIRES OF FOREVER by Chad Oliver: Irth was slipping backwards to extinction, and only a few scientists were left to seek the help they needed from the stars. They had a Ship--and an ancient Skull. With those, they had to win!