The Emergence was a type of ceremony done by the Black Robed Wizard, Maddoc, to awaken Asvoria's soul that was trapped in the body of the Young Adventurer, Nearra.
Maddoc planned to cause the Emergence by threatening Nearra's life in hopes that the stress would release Asvoria to the world, where he could control her. He cast a spell upon Nearra before the Emergence that would paralyze the body if Asvoria did emerge.
The Emergence happened in 354 AC on the roof of Cairngorn Keep. Despite the best efforts of the Young Adventurers, the sorceress Asvoria was freed. She possessed Nearra's body and escaped Maddoc's grasp and control using the mystic amulet, the Daystar. Asvoria left the keep intent to conquer Solamnia this time around.
References[]
Temple of the Dragonslayer, pg. 64
The Dragon Well, pg. 4
Return of the Sorceress, pg. 38, 234, 236