A Warhammer 40,000 novel.

The Emperor's Spears are a Chapter on the edge of destruction, last watchmen over the Elara's Veil nebula. Now, the decisions of one man, Amadeus Kaias Incarius of the Mentor Legion, will determine the Chapter's fate.... 

Listen to it because:

Aaron Dembski-Bowden has turned his attention to creating (and maybe destroying) a Space Marine Chapter in detail, and this is your chance to discover their fate.  

The story: 

The scattered worlds of the Elara's Veil nebula were once protected by the oath of unity sworn by three mighty Chapters of the Adeptus Astartes. The Star Scorpions were undone by flaws in their genetic coding. The Celestial Lions were ravaged by the Inquisition for sins they did not commit. Now, after hundreds of years, only the Emperor's Spears still keep their vigil. They are barbarian watchmen against the Outer Dark, bloodied but unbroken in their long duty.  

Amadeus Kaias Incarius, a brother of the Mentor Legion, is commanded to cross the Great Rift and assess the Spears' war-readiness, only to be drawn into the chaotic plight of a depleted crusade on the Imperium's benighted frontier. The decisions he makes, far from the God-Emperor's light, will decide the fate of the war-torn Chapter.  

Written by Aaron Dembski-Bowden. Running time 11 hours and 46 minutes. Performed by Kelly Hotten.