The Paradox War — Ian C. Douglas

Mars has fallen and Earth is next. As the Spiral tightens its deadly grip on humanity, Fitch Crawley serves as a murderous emissary. No one can stop them. Least of all Zeke Hailey, on a far-flung moon, resurrected but his memory wiped clean. Never has Zeke more needed his best friend, but Scuff Barnum is gone. Hurled billions of years back in time. Scuff is trapped with the ancient Martians on the eve of the calamity that destroyed them. Could he change prehistory or is he doomed to perish in a fiery apocalypse? Zeke struggles to cure his amnesia, aided by a mysterious scientist and aliens. But even if Zeke recovers, what chance has he of returning to Mars for one last stand? Now that the colonists are dead and only robots and monsters remain. Truly, the Spiral will kill all life in the universe.