Enemies of the Imperium (2013), p108 — Sisk

The world of Sisk resonates in the Warp like a finely tuned chord. Several Chaos warbands have seen fit to intervene from time to time on Sisk, and there exists a handful who have made the planet their home base in the region. A deep thread of heresy and genetic corruption has poisoned much of Sisk's population, aided by whispered lies and seductive promises from the lips of Dark Apostles. The warbands operating on Sisk have set their goal as the slow and gradual corruption of the entire planet. Many of the mutants lurking in the planet's mist-ridden highlands have sworn dire oaths to the Dark Gods, and a surprising number of nobles in the Lord Governor's court have joined them. The Governor, Lord Gavvit, remains mostly unaware of these plots and schemes amongst his own followers, but he has begun to suspect that the "mutant problem" far from his capital is much more severe than anyone truly understands.

A great swamp on the southernmost continent has recently come under the sway of Malaghent, a Chaos Lord who has dedicated himself to the foul embrace of Nurgle. In the burbling depths of the marsh, Malaghent has begun a horrific breeding program amongst the mutants, attempting to use his own noxious sorcery to create a new strain of mutation, capable of spreading his patron's gifts of plague and filth far and wide. So far, patrols on Sisk are completely unaware of Malaghent's location, but the misshapen results of his experimentation have begun to acquire notice amongst the Imperial Guard advisors in the region. At least one platoon of Valhallans have gone missing in this area, and it is only a matter of time before the Imperium's military takes a much greater interest.