Ahriman - Fall of Prospero: Magnus next attempted to forewarn the Emperor of the impending betrayal of His favourite son. However, knowing that he would have to find a means of quickly warning the Emperor, Magnus used sorcery to telepathically send his message to the Emperor. The message penetrated the potent psychic defences of the Imperial Palace on Terra, shattering all the psychic wards the Emperor had placed on the palace -- including those within His secret project in the Imperial Palace's dungeon, where He was proceeding with the creation of a Human extension into the Webway.Refusing to believe that Horus, His most beloved and trusted son, would actually betray Him, the Emperor instead mistakenly perceived the traitor to the Imperium to be Magnus and his Thousand Sons, who had long suffered from a near-debilitating run of mutations because of the instability of Magnus' own genome as well as being practicioners of sorcery that brought them into constant contact with the dangerous entities of the Empyrean.The Emperor ordered the Primarch Leman Russ, Magnus' greatest rival, to mobilise his Space Wolves Legion and the witchhunters known as the Sisters of Silence, alongside a contingent of the Emperor's own Legio Custodes, and take Magnus into custody to be returned to Terra to stand trial for violating the Council of Nikaea's prohibitions against the use of sorcery within the Imperium.While en route to the Thousand Sons Legion's homeworld of Prospero, Horus convinced Russ, who had always been repelled by Magnus' reliance on psychic powers, to launch a full assault on Prospero instead even though Magnus had been entirely willing to face the Emperor's judgment once he realised he was being manipulated by the entities that called the Immaterium home.Amon's loyalty and confidence in Magnus was severely shaken when he discovered that his primarch had murdered Baleq Uthizzar, the captain of the 5th Fellowship and leader or "magister templi" of the Athanean Cult, for knowing too much about the impending assault by the encroaching Space Wolves Legion. Taking Amon into his confidence, the primarch and his former tutor travelled the Aether together in their astral forms. Magnus showed Amon the approaching fleet of the VIth Legion.He admitted to his former tutor that he had been wrong about everything. All the things that Amon had taught the adolescent primarch had been arrogantly dismissed out of hand, for Magnus presumed he already knew. He had been warned by Amon about the gods of the Warp, which the primarch had rejected, calling his tutor a superstitious old fool.The primarch confessed that he had done terrible things, but he tried to convince Amon that he had done them for the right reasons. Magnus had drawn a psychic veil around Prospero. None could see out as their punishment drew closer, not even the sorcerers of the Corvidae Cult. Magnus accepted his punishment for his hubris, and would sit by and do nothing as his Legion was wiped out for their violation of the Emperor's Decree Absolute at Nikaea.Amon could not abide his primarch's decision, whether it was the right thing to do or not. He could not sit idly by and accept the inevitability of the Thousand Sons' pre-ordained destiny. Magnus explained to his oldest friend the reason that he had not struck at the Space Wolves was because it was what the Ruinous Powers had wanted him to do since he had first come to Prospero by their design. The Chaos Gods wanted Magnus to take arms against the Thousand Sons' doom, knowing that if he did, it would only confirm everything those who hated and feared the Thousand Sons had always believed.In that moment of his primarch's dire revelation, Amon confessed to his gene-sire that before Magnus had come to Prospero he had suffered a recurring nightmare. Amon had dreamt that everything he held dear was swept away and destroyed. It plagued him for years, but on the day the infant primarch had arrived from the heavens like a comet, the dream stopped. He never had it again. Amon convinced himself that it was nothing more than an ancestral memory of Old Night, but it was not. He knew that now, for he had foreseen this moment in time. The destruction of everything he held dear was coming to pass.Despite everything Magnus had done, the primarch still believed that his fate was his own. He was a loyal son of the Emperor, and he would never betray Him, for the primarch had already broken His father's heart and His greatest creation, the Terran Webway extension. Magnus intended to accept his fate and though history might judge the Thousand Sons as Traitors, at least Magnus and his sons would know the truth. They would know that they were loyal unto the end because they accepted their fate. Magnus now urged Amon to do the same. But Amon refused to acquiesce to his gene-sire's wishes. He would not sit passively by, waiting to die like some infirm, decrepit animal. Amon intended to fight for his people and his home.After the Space Wolves' Retribution Fleet translated in-system, they proceeded to destroy Prospero's orbital defences. They then commenced a tremendous orbital bombardment that reduced Prospero to cinders, except its capital, Tizca, a beautiful city and the seat of Magnus and the XVth Legion, that was at all times protected by a powerful psychic kine-shield. This shield was maintained by one of the Thousand Sons' sorcerous cults, and Magnus did not disable it, knowing that such action would alert his Legion.Because of the telekinetic shield, an Imperial ground invasion of Tizca had to take place. A huge force of landing vehicles and support craft descended on the city, whose defences had been left mostly unmanned. Establishing a beachhead in the city's spaceport, the Space Wolves began slaughtering thousands of Prosperines and burning everything in sight. Yet the Thousand Sons' rank-and-file did not share Magnus' acceptance of defeat and punishment, so they took up arms against the Imperial invaders. The Thousand Sons managed to hold Tizca (the only surviving city on the planet) for a period of time before they were eventually pushed back.Before Magnus reluctantly faced the wrath of his brother, Leman Russ, he entrusted Amon with a precious gift, his most prized possession, the Book of Magnus. This massive tome contained the collected Human knowledge of sorcery as dictated by Magnus. It was said that this work was one of the most complete treatises on psykers, witchcraft and sorcery in the galaxy, a compilation of all the knowledge and experiments gathered by Magnus during the conquests the Thousand Sons made for the Imperium during the Great Crusade.Amon was charged with its safekeeping and to ensure that it was passed on to Chief Librarian Ahriman. Magnus eventually, reluctantly, took to the battle against the Imperial forces when Leman Russ and his Wulfen were unleashed on the last glass-and-steel pyramid of Tizca still standing.At the height of the battle, Magnus and Leman Russ took part in a devastating duel in which Russ was ultimately victorious. Mortally wounded, with his back broken, Magnus invoked ancient sorceries in order to escape Prospero by opening a gateway through the Warp into the Eye of Terror where a Daemon World (Sortiarius, the Planet of the Sorcerers) had been prepared for Magnus and the remnants of his Space Marine Legion by their new patron god, Tzeentch. Magnus was subsequently "rewarded" by Tzeentch by being transformed into a Daemon Prince.