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At dawn on Higharvestide of 1369 DR, two members of the Twisted Rune managed to kidnap Halaster Blackcloak from inside Undermountain. The lich Priamon "Frostrune" Rakesk and the alhoon Ralayan the Occultacle used a ring of multiple wishes to bind and summon the Mad Mage to Stardock, where they intended to probe the great archmage's mind for his intricate knowledge of portals and magical gates. Before being captured, Halaster sent out a sending to all practitioners of the Art within 400 miles, a clue that could lead would-be rescuers to where he was held. It said "Seek me at Aquitiocun!" The sign of the Mad Mage appeared as a 75-foot-diameter (23 meters) floating sigil of black flames in the harbor, blocking all traffic until it dispersed at highsun.
Because Halaster was the eye of the storm that was Undermountain, his kidnapping allowed the madness of the dungeon to escape. Gates began randomly transporting creatures from Undermountain to places throughout the Realms, causing havoc and destruction everywhere. Among the many events, fire salamanders destroyed parts of Luskan, a gorgimera and manticores attacked Shadowdale, a legion of gargoyles laid siege to Suzail, and a juggernaut formed from shipwrecks flattened the pirates' Port of Skaug. But by far the greatest amount of mayhem spilled out into the city of Waterdeep itself.
A group of adventures hired by the Lords of Waterdeep managed to reach Stardock and free Halaster. The Mad Mage immediately returned to Undermountain, which quelled the chaos of the dungeon and ended the terror of Halaster's Higharvestide within hours. The two mages of the Twisted Rune fled Undermountain by means of teleport spells before Halaster's rescuers could attack them.