Opal is a gleaming shrine world of saints and soldiers, beloved of the Emperor Himself. Sent to retrieve the skull of the revered Saint Veres, Sister Superior Augusta of the Order of the Bloody Rose and her squad find themselves in the midst of the capital's holiest festival, a time of reverence and celebration. But all is not well – despite what its planetary leaders would have Augusta believe, political danger bubbles under the surface, and rebel attacks gnaw away at the city's outskirts. The greatest threat, however, is yet to come.

As it becomes horrifyingly apparent that a Genestealer Cult has its claws under the planet's skin, the Sisters realise that can mean only one thing: a hive fleet is on its way to Opal, bringing with it the planet's doom.