The story of Diablo II takes immediately after the end of Diablo (and also in Sanctuary), where the Warrior character of the first game tried to contain Diablo within himself by plunging the Soulstone into his own head. Unfortunately, he was instead corrupted by the Lord of Terror, and became the Dark Wanderer. Despite struggling with the demon within, he spread chaos and terror wherever he went. Diablo had in fact planned this all along, luring the Warrior to his dungeon.
The player takes on the role as one of five (seven in the expansion) heroes who group up in order to stop Diablo and the other Prime Evils. They start in the Rogue Encampment (which may be in Entsteig or Khanduras, the lore is fuzzy), chasing after this mysterious Dark Wanderer who had summoned demons to overrun their monastery, which guarded the passage to the East.
Diablo leaves hinders for the heroes, such as the Lesser Evil, Andariel, in the Monastery, and heads first to the Aranoch desert to free his brother Baal near Lut Gholein, and then further to the jungles of Kehjistan to free Mephisto under the city of Kurast. At every step of the way, the player not only chases Diablo, but also has to deal with demonic corruption and other obstacles in the way.
Finally, the heroes catch up with the Brothers, and kill Mephisto in Travincal, ending the corruption of the Zakarum Church, and goes through a portal to Hell itself, to find Diablo.
Searching hell, and finding the Chaos Sanctuary, Diablo's home, the heroes summon the demon before he has fully recovered from transforming into his real, red, self, and defeats him. The heroes are then charged with destroying the Soulstones as the Prime Evils were taught long ago how to corrupt them by the fallen angel Izual.
The story continues in the expansion to the game, where the player chases the last of the Prime Evils; Baal (Lord of Destruction) who is going after the mythical Worldstone in an attempt to corrupt it.
