Battle Group Purgator was formed when Inquisitor Lord Scallen discovered the existence of a Chaos cult on Therrix Prime. He swiftly acted with his household troops to destroy a number of the cult's small cells. But interrogations of the captives revealed a far deeper heresy than he had guessed. Scallen, calling upon the Imperial Guard Mordant 808th regiment, launched larger assaults against key cult strongholds. Having suppressed the cult's leadership only lead to the cult's lower echelons rising up, and soon Therrix's hives were all plunged into bloody anarchy. All Space Marines in the region were called upon - the Subjugators, Mentors and Novamarines responding with aid. In the final stages of the rebellion Scallen feared the cultists might draw forth a full-scale daemonic invasion, so he initiated and lead a major assault against the final cult stronghold located in the depths of Hive Tumulus. The Battle Group was joined by a mysterious unrequested Vindicare Assassin, and also, upon hearing of the cult's blasphemies, the entire Order of the Bloody Rose of the Sisters of Battle backed by a delegation of the Adeptus Ministorum. Overwhelmed, the remaining survivors of the cult fled from the hive in an armored column. But Scallen had foreseen such a move and called upon two Warhound Titans from the Legio Ignatum. The transports were intercepted and destroyed, crushing the cult for all time.