The Traitor's Hand (Ciaphas Cain Book 3)

Ciaphas Cain's latest missions takes him and his Valhallan regiment to the planet of Adumbria to defend against an approaching Chaos invasion. However, infighting with fellow Imperial Guard regiments and the uprising of a sinister cult on the planet puts paid to any hopes of an easy life.

Read it because
There's an insight into Commissar Cain's past as we meet an old "friend" from his Schola Progenium days, and the commissar faces his toughest test yet: avoiding the temptations of a Slaaneshi pleasure cult...