The Double Invaders by John Rackham / These Savage Futurians by Philip E. High (Ace Double)

Paperback. Condition: Good+. 1967. Ace.

The Double Invaders:

This story tells the tale of the invasion of the planet Scarta by ships of Zorgan. The initial invasion plan goes like it should, and the key cities of Scarta are taken. However, the Scartans don't act like they've been conquered, and the Zorgan seem to be overconfident.

Resistance continues across the planet. The Zorgan take this in stride, just raising the output power of their weapons a notch at a time. Zorgan seems to have everything under control until the Zorgan ships start to disappear...

The Savage Invaders:

Don't think new thoughts, don't improve anything, don't wander over the next hillthese were the commandments for the men and women of the experimental village - one of those careful nurtured settlements established after the collapse of world civilization. The rules were made by the benevolent Masters of the Island - and they had to be obeyed. To disobey was to be destroyed. But Robert Ventnor, villager with a dangerously high quotient of curiosity, was the exception. He fled - and evaded liquidation. But he fled right into the hands of THESE SAVAGE FUTURIANS and thereby supplied the key that could blast apart civilization's second chance and destroy the world once and for all.