The Ganymede Takeover by Philip K. Dick & Ray Nelson

Paperback. Condition: Fair (Reading Copy). 1967. Ace. 

First published, in paperback, in 1967, this is one of two novels Dick wrote in collaboration. Earth has been taken over by a strange alien force - creatures whose instinct for survival overrides any human resistance. Then a vital weapon - with the power of electronically warping the mind - falls into the hands of a terrorist group still strong enough to oppose the aliens. A weapon so powerful that it cannot be controlled. The control of Earth is in the balance - and the balance is a terrifyingly precarious one.