Nightbringer (Warhammer 40,000 Novels)

Newly promoted Ultramarines Captain Uriel Ventris is assigned to investigate Pavonis, an Imperial planet plagued by civil disorder and renegade eldar raiders. But nothing is as straightforward as it appears, and wheels are turning within wheels. Uriel and his allies are forced into a deadly race against time to destroy their shadowy enemy - or the whole planet must be sacrificed for the good of humanity.