SF. Ace Double- Brian W. Aldiss "Bow Down to Nul" / Manly Wade Wellman "The Dark Destroyers"

The Dark Destroyers - Manly Wade Wellman.

Slimy ice-cold creatures had taken over the world in one brutal blitzkrieg, and after fifty years of their domination the only humans left were living like animals in the deepest tropical jungles.   Mark Darragh, a brash young man dreamed of the world his fathers had lost and travelling by flimsy canoe, started out for the Cold People's stronghold - all he had to lose was his life.

Bow Down to Nul - Brian W. Aldiss.

When Earthman Gary Towler is off work, he is a pariah.  For his task as chief interpreter for the corrupt and tyrannical nuls makes other humans avoid him as a traitor.  Nor is he trusted by the three-amred mammoth rulers themselves, especially when they learned that an envoy was on the way from their distant planetary headquarters to investigate charges of corruption on Earth.  The leaders realized that Gary knew too much.

A 1960 Ace paperback in fair to good condition based on the Hancer Standard.