The Call

The Call refers to a phenomenon in The Places Below. For 3 years, from 1192-1195, a mindflayer had hijacked the Drow Horn communication system, infusing its messages with psychic energy, and drawing all who heard it to the ruins of Dar Haggrifar. He amassed an army at Dar Haggrifar, and used the magical secrets of the city to prepare weapons both mundane and magical. He supported his operation through funneling magic items to the surface, and using the gold earned, importing food to feed the drow under his dominion.
After his army was amassed, the goal of the mindflayer was to conquer the Dwarfic Axis, and use their industrial capacity to produce an army of clockwork soldiers, which would then be used, with the army of enthralled Drow and Dwarves to invade the surface, and take over all of Asurus.
The mindflayer's plan was stopped by the party known as the Slaughterer's of Shiptoast, in a campaign lasting 3 years, and going from level 1 to level 18. They eventually killed the elder brain in charge of the operation in Lair of RishGol.