Throneworld - Guy Haley

The Imperium's situation has never been more grim - an ork attack moon hangs over Terra, and ork armadas ravage human space. To make matters even worse, eldar strike at the heart of the Imperial Palace, forcing humanity's defenders to fight on two fronts at once. Though it seems nothing can stop the orks - neither brute force, science, nor faith - an unlikely alliance in the furthest reaches of space uncovers the first clue how to defeat the greenskins. The Adeptus Astartes now face an almost impossible task - taking news of this discovery back to Terra through a galaxy teaming with orks.