The God Mars Book Seven: Earthside - The God Mars, #7

The God Mars is a pulp-style science fiction series set in a rich world of varied cultures and colorful characters. The series plays out on a partially-terraformed Mars, a half-century after a man-made disaster cut thousands of colonists off from Earth, and the fear of a rampant nanotech plague discouraged rescue. Left to survive for generations with few resources, the various groups develop unique new cultures at different levels of technology, ranging from the primitive to the frighteningly advanced.
But all are now trapped in an escalating war between an oppressive Earth that's terrified of potentially infectious nanotechnology, and invincible superhumans who claim to have come from a nightmare future caused by that same technology. In Book Seven: Earthside, Colonel Ram has been translocated to Earth against his will to stop the technological demon Asmodeus, who has made his own way there, intending to wreak havoc on that completely vulnerable planet of ten billion souls for his own sadistic amusement.
But both find an Earth that's been changed by tragedy and social upheaval beyond anything they'd imagined, into an enforced utopia that neither can bear. And that utopia will do anything to protect itself.