Empire Rising. Earthfleet Saga, #4

Once thought destroyed, a dangerous enemy has returned, bringing with them weapons of immeasurable power to finish the job they originally failed to complete. Attacking from the shadows, they threaten to destroy and conquer the galaxy one race at a time and bring the new Galactic Alliance to its knees. To stop this threat, the Alliance, the Society and the nine races must work together to find this enemy and destroy them before they can achieve their goal of galactic conquest.