Lost Fleet - Victorious (Book 6) - Campbell, Jack

As war continues to rage between the Alliance and Syndicate Worlds, Captain 'Black Jack' Geary is promoted to admiral-even though the ruling council fears he may stage a military coup. His new rank gives him the authority to negotiate with the Syndics, who may finally be willing to end the war. But an even greater alien threat lurks on the far side of the Syndic occupied space.