The Carrion Throne (Vaults of Terra #1)

Inquisitor Erasmus and his acolyte Spinoza root out a shadowy conspiracy on Holy Terra itself, the capital world of the Imperium.

In the hellish sprawl of Imperial Terra, Ordo Hereticus Inquisitor Erasmus serves as a stalwart and vigilant protector, for even the Throneworld is not immune to the predations of its enemies. In the course of his Emperor-sworn duty, Erasmus becomes embroiled in a dark conspiracy, one that leads all the way to the halls of the Imperial Palace. As he plunges deeper in the shadowy underbelly of the many palace districts, his investigation attracts the attention of hidden forces, and soon Erasmus and his acolyte Spinoza are being hunted – by heretics, xenos, servants of the Dark Powers, or perhaps even rival elements of the Inquisition itself. They eventually discover a terrible truth, one that if allowed to get out could undermine the very fabric of the Imperium itself.