1963 Printing - Priced for vintage book The underground people of Earth were united in terror and desperation against what they considered a frightful threat from the skies. They had sent a mighty armada into space, rushing in lethal orbit toward Mars. The Spacers --- still really Earthmen themselves --- were poised for the counter-blow. The great fleet at Asteroid Central had sufficient warheads to reduce Earth to a cinder. But there was a third force, watching . . Pyramid F-933 is the First paperback printing, 1963