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.
Book four in the Ciaphas Cain series by Sandy Mitchell.
Excellent and a good fun light read. However, is actually the third in the series and not, as the iBooks description days, the fourth.