Ahriman - Siege of the Fenris System: Sometime before the start of the 13th Black Crusade in 998.M41, Ahriman was summoned back to the Planet of the Sorcerers by Magnus the Red himself for the first time since the casting of the Rubric of Ahriman. Magnus agreed to once again work with Ahriman towards a common goal. During the subsequent Siege of the Fenris System, the two fought together in mutual vengeance against the hated Space Wolves.Shortly after reuniting with their long-lost Wulfen brethren, the Space Wolves found their home system engulfed by raging Warp Storms and a massive daemonic invasion. The Grey Knights and Dark Angels arrived to aid the Sons of Russ in expelling the threat, but the Imperial forces were coerced into a state of infighting by one of Tzeentch's most devious Daemon servants -- the Changeling. It was the Grey Knights who first noticed the Warp Storms forming a pattern, one recorded in their oldest tomes of lore and not seen in the galaxy for ten thousand standard years. It was a symbol of vengeance last used on Prospero by the Thousand Sons.As the home system of the Space Wolves was overrun by Daemons, nine Silver Towers appeared in the skies above Fenris. From their warped halls poured ranks of Thousand Sons, ready to wreak vengeance on the Chapter that destroyed their homeworld. Swarms of braying Tzaangors and mutated Chaos Cultists charged across the frozen plains, with Rubric Marines and Scarab Occult Terminators marching close behind.From hidden portals more Thousand Sons emerged onto the Fenrisian steeps, exiles brought back into the fold by Ahriman. By following the Arch-sorcerer through the Webway they were able to take the Space Wolves and their allies by surprise, incinerating the Adeptus Astartes with crackling psychic energy as they burst from the Labyrinth Dimension, guided by the knowledge of that realm that Ahriman had stolen from the Black Library.As the Imperial lines held out against the onslaught, the Silver Towers aligned with sites of geomantic power and began siphoning the internal energy of Fenris, and on the third solar day of the invasion the air was riven with fire. Sorcerers around the planet poured their psychic energy into this sky-fire, and within each of the Silver Towers a captive Space Wolf was boiled alive in a cauldron of gore.This conflux of dark magics created a weak point in reality -- a doorway through which strode the Daemon Primarch Magnus himself. The Crimson King joined with Ahriman and his other most powerful acolytes, and together they began their rituals in the hearts of the Silver Towers. The resultant flow of mutagenic energy ravaged the surface of Fenris, causing the molten magma powering the Space Wolves' fortress-monastery, The Fang, to fill with Daemons and bubble up to the surface.It was only when the neighbouring planet of Midgardia was destroyed that the Silver Towers disappeared from the Fenris System, but any Imperial celebration was premature -- unbeknownst to the Space Wolves, the psychic harvest reaped by the towers from Midgardia's demise had given Magnus the power he needed to enact a plan of unimaginable scope -- the return of the Planet of the Sorcerers to realspace, where it now sits in orbit above the husk of lost Prospero.