Guardian of night

the long version

"Captain Arid Ricimer, an alien starship commander with integrity and a clever plan, attempts to defect to Earth with his officers and entire spaceship, a vessel that mounts a superweapon of almost unimaginable power. He's pursured by his former fleet, a force that has already devastated Earth and is poised to wipe out humanity from existence. Now Arid, along with his human allies, Captain Jim Coalbridge and alien analyst Lieutenant Commander Griff Leher must face down the forces of a tyrannical star empire"--