Invincible: Ark Royal, Book 12 (Unabridged‪)‬

All is not well in the Human Sphere. The alliance between the Great Powers is starting to fall apart, the human economy cannot keep up with the urgent need for newer and better starships, and politicians are demanding an end to military spending. For the Royal Navy, desperately trying to do too many tasks with too few ships, it is the worst possible time for a new threat to appear. 

When a generation starship is detected approaching a British colony world, HMS Invincible is dispatched to intercept the aliens before they can make landfall. But the newcomers bring with them tidings of a new and deadly threat, an expansionist alien race far too close to the Human Sphere for comfort...and a sinister horror beyond human understanding.