The Raid on the Temple of Asmodeus

From publisher blurb: Raid a temple of evil to fight a pit fiend in this 20th level adventure for the world's greatest role-playing game. A pit fiend named Axanthazel, who is a servant of Asmodeus, is to lead an army that is setting out to destroy many of the cities of humans. The pit fiend is at this moment in the Temple of Asmodeus in the evil city of Achelous, and you have been asked to go on a special mission to raid the temple. You must recover the war plans and kill the pit fiend if you can. If you do not stop Axanthazel, then Asmodeus's evil will overrun the continent of Aduial.