The House in November — Keith Laumer

Invasion! At first the U.S. army - what was left of it - thought it was battling a communist invasion. The truth was much worse. It wasn't until Jeff Mallory awoke one morning to find that all his fellow townsfolk had become sleep walking zombies, and that a tower had been erected in the center of town, a tower that seemed to stretch to the stars, that the horrible truth began to unravel. Earth had been invaded - not by a race of alien conquerers, but by a disease. A disease with a brain...