After releasing one of Demogorgon's ex-lovers, Shami-Amourae, from her prison in the Wells of Darkness, the heroes endured a brutal counterattack by the the Prince of Demons' forces that included a catastrophic redirection of the Ruver Styx. Enraged at this affront, Charon himself arrives not long thereafter to investigate and grants the heroes passage on the River Styx if they promise to punish Demogorgon for his audacity.
Using the River Styx, the heroes travel across the Abyss, Hades, and Arborea, recruiting powerful agents in the battle to come against the Prince of Demons. As their allies mount, though, Demogorgon grows concerned, and as the heroes near the completion of their task, he sends a force from his armies to deal with them. Assuming they survive, the heroes are now prepared to launch their assault on Gaping Maw.