Dan Abnett
The Armour of Contempt
Gaunt's Ghosts (series) part 10

Gaunt returns with the Tanith First to a world that he promised to save, only to find that years of war and the ever-present taint of Chaos may have damaged it beyond redemption.
Warhammer 40k
novel

Also in:
Sabbat Worlds: the Digital Collection
The Lost