Forge Master (Space Marine Battles Novella)

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

Read it because
It's the dramatic conclusion to the Overfiend trilogy and sees the Salamanders burn into action aboard an ork warship.