James Swallow
Red & Black

When a mysterious messenger contacts the Adepta Sororitas, Celestian Miriya must travel to Hollos and pass judgement on the world. Will she find a world embracing the Emperor’s truth or one in need of cleansing? Her decision will liberate or condemn an entire planet.
Warhammer 40k
novel

Also in:
Sisters of Battle: the Omnibus
Crusade + Other Stories