Warhammer 40k Watchers Throne Novel

"The Custodian Guard have stood watch over the Emperor's Palace on Terra since the foundation of the Imperium. Charged with protecting the Master of Mankind from all threats, within and without, their fearsome resolve is renowned throughout the galaxy, and their golden armor is the last thing that a would-be assassin or saboteur will ever see. Alongside the Null-maidens of the Sisters of Silence, who are anathema to psykers and sorcerers alike, there is no threat to the Golden Throne that they alone cannot vanquish... until now. "