The Sagittarius Command (Tour of the Merrimack Series #3)

After the finest battleship-class spaceship in Earth's fleet, the U.S.S. Merrimack, rescues a near-space Roman world besieged by a destructive alien life-form known as the Hive, the Romans' leader, Caesar Magnus, insists on honoring the ship's captain, John Farragut. But when Caesar is assassinated, Farragut must lead a mission into the heart of Hive territory in search of a Roman who has been presumed 'dead' for decades.