Necessary Evil is a short story by Rob Sanders. It was originally published in Hammer and Bolter 23, and re-published online in August 2015.
Inquisitor Bronislaw Czevak - scholar, adventurer, fugitive. Since fleeing the fabled Black Library of the eldar with the Atlas Infernal, he has been hunted by xenos, heretic and sorcerer just as he once hunted them. Guided and protected by this ancient tome bound in human skin, he has now found his way to the daemon world of Nereus in search of a powerful Chaos artefact. With Ahriman and the Thousand Sons racing to claim it for themselves, Czevak must scour the colony of Perdition's Landing if he is to outwit his old enemies... but might this bedraggled outpost hide an even darker secret of its own?