Vanguard

"Earth is no longer the center of the universe. After the invention of the faster-than-light jump drive, humanity is rapidly establishing new colonies. But the vast distances of space mean that the old order of protection and interstellar law offered by Earth has ceased to exist. When a nearby world attacks, the new colony of Glenlyon turns to Robert Geary, a young former junior fleet officer, and Mele Darcy, a onetime enlisted Marine. With nothing but improvised weapons and a few volunteers, Geary and Darcy must face down warships and armored soldiers--or die trying"--