Plague Zone — Jeff Carlson

First Earth was devastated by the machine plague, -- a runaway nano-technology that devoured all warm-blooded organisms below altitudes of ten thousand feet. Then the remnants of humankind turned on one another, provoking a brief, furious world war and the invasion of North America. Now Russian and Chinese armies hold California against the battered forces of the U.S.-Canadian Alliance.

Nanotech researcher Ruth Goldman and Cam Najarro -- a former Army Ranger who helped her force an end to the war -- have finally found some peace in a small, hidden village in the Rockies. But the arms race for weaponized nanotech has continued, and America is struck by a new contagion.

Together with a small band of friends and rivals, Ruth and Cam must discover the source of the new plague -- never suspecting that its creator is an old enemy they believe dead...