Warhammer 40k - Space Marine Battles Novella - Forge Master by David Annandale

As the war against the orks of the Octavius system grinds on, the Fifth Company of the Salamanders are assigned a dangerous – and critical – mission: to kill the Overfiend himself. But as they prepare to annihilate the beast’s ship, they discover a startling secret: that a valuable – and dangerous – alien prisoner aboard the ork warship may be the key to ending the conflict.