Para Bellum — Christopher G. Nuttall

On her last mission, HMS Invincible discovered an alien threat beyond human understanding: a sentient virus that has already absorbed a number of intelligent races into its multitude and now intends to do the same to humanity. Defeat means the end of everything, the end of existence as nothing more than mindless host-bodies, the end of humanity and its alien allies alike. The stakes could not be higher.

As a deeply divided humanity struggles to prepare a defense, with enemies inside and outside the human sphere just lurking to strike, Invincible is sent deep into alien space on what should have been a simple reconnaissance mission. But, as Captain Shields and his crew begin their mission, it rapidly becomes clear that a juggernaut is bearing down on Earth....

And, no matter what they do, they may never make it home again.