Scouring of the Coven

The Scouring of the Coven was a lamentable event that occurred in the history of the Penitent Knights Chapter. When the bulk of the Chapter was away on crusade, the nefarious Drukhari took advantage of the situation and attacked the Penitent Knights' home system, including their Chapter homeworld of Lor'dra, spiriting thousands of unfortunate humans away, to force them into a live of slavery. They arrived, too late, to make much of a difference. This event remains a mark of shame upon the Penitent Knights' glorious deeds.

History
There was a brief time in the thirty third millennia when the Penitent Knights had deployed most of their Chapter to Crusades and wars away from their home System, and this time was exploited by a wicked and hedonistic Drukhari Kabal who raided and abducted many Lor'dranian natives from the planet while the Knights were away. This Kabal, known as Tainted Blood, were accompanied by strange fire-wreathed constructs that did their diabolical bidding like servants. When the Order of the Gryphon returned from a forgotten Crusade in the Gothic Sector, they arrived too late for many of their subjects and instead hatefully destroyed every Drukhari they could, before the xenos fled to the Webway with many humans as their slaves. To this day, the Knights see the grievous failure as a sin that must be removed with as much xeno blood as possible.