Return of the Forsaken

The Return of the Forsaken was a lamentable campaign in the history of the Hammer Guard Space Marine Chapter. Just under two centuries after the Chapter's 5th Company disappeared in the warp rift known as the Maelstrom, during the three-century long Penitent Crusade known as the Hammer's Wrath. It was revealed that the 5th Company had not only survived, but had been wholly corrupted by the influence of Chaos. When they were discovered by the 2nd Company, they influenced their fellow brethren and wholly corrupted them, forming the infamous Chaos Warband, the Forsaken Hammers.

History
The fate of the 5th Company was revealed in 979.M41, when the 2nd Company was deployed to a lost Agri-World to purge the forces of Chaos that had emerged there, using it as a base to raid other systems. Instead of finding a world full of cultists and the Word Bearers, who they had suspected to be their foe, the 2ndCompany found Astartes wearing their heraldry and livery. These mysterious Astartes welcomed the 2nd Company, telling them they have been found, and congratulating them on discovering the true path. Lured into this trap, legate Decarde Karrova and his company were corrupted, the "Forsaken Hammers" as they called themselves, showing the 2nd Company the "Truth of the True Stars" and the "Lies of the False Star."