After the devastation of Baal, Mephiston leads a squad of Blood Angels to a war-torn world near the Great Rift, following mysterious visions. Here, the sorcerers of the Thousand Sons seek to unite the nine Silver Towers and perform a ritual that will grant colossal power to their master, the demonic primarch Magnus. The ritual must be disrupted, otherwise the entire sub-sector will plunge into chaos. Mephiston faces an unprecedented challenge that will test his strength and will. He must discover a truth that threatens to expose his darkest fears.