Board Thread:Warhammer 40k Novels/@comment-5597699-20121008214512/@comment-3258762-20131029195612

Ziebro wrote: I would like book where either an Arbiter or Inquisitor is trying to solve some mystery involving Chaos, xenos, or both. The only one that is directly about that that I know is Emperor's Mercy.

However, I didn't particularly like that novel.

If you're a bit more liberal about the content, you can try the Eisenhorn series.