Victorious (The Lost Fleet, Book 6 of 6)

the long version

The Lost Fleet: Relentless found its way onto the New York Times bestseller list...Now Victorious leads the charge again-and "Black Jack" Geary is in command... 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 have suffered tremendous losses and may finally be willing to end the war. But an even greater alien threat lurks on the far side of the Syndic occupied space.