THAT WAS NOW, THIS IS THEN

Novel. Then: First Lieutenant Elliot and nine other soldiers were thrown back to Earth's Paleolithic Age. Against all odds, the team survived and found their way back to the 21st-century. Now: The Bykos, humans from the far future whose meddling caused the first rift, have stranded another group of soldiers in the past. Elliot's team needs to go back to rescue them.