Extremis: Starfire, Book 6

An implacable foe with telepathic cohesion in battle, near immortality, and eons-advanced engineering skills threatens to wipe humanity from the galaxy. What's more, they've overcome their one weakness - no faster-than-light travel - and have followed humanity through our star gates and beyond. But humans are the master of adaption and have got a counterpunch of devastating proportions in reserve. Now a hard-bitten and brilliant admiral must face down renewed alien attack and somehow communicate to the enemy that if he is forced to use his ultimate military option, galactic civilization itself may come to a fiery end.