As you journey through the lands of Sanctuary, you are joined by Leah and her mother, the witch Adria, to find the . This powerful artifact was designed by the renegade mage Zoltun Kulle to trap the souls of all seven Great Evils—including the already-defeated Prime Evils—simultaneously.
Diablo launches an assault on the High Heavens, nearly destroying the Diamond Gates. You eventually confront and defeat him at the pinnacle of the Silver Spire.
The story of Diablo 3 begins with a literal "fallen star" crashing into the Tristram Cathedral, a portent that sets the stage for a grand struggle between the High Heavens and the Burning Hells. The Fallen Star and the Stranger
After you successfully trap the final two Lords of Hell, Belial and Azmodan, the truth is revealed: Adria has been a servant of Diablo all along.