Diablo II: Lord of Destruction is an expansion pack for the hack and slash action role-playing game Diablo II.
After the player successfully ventures into Hell and defeats Diablo in Act IV, upon returning to the Pandemonium Fortress they are met by the Archangel Tyrael with an urgent summon.
Tyrael opens a portal to Harrogath, a stronghold on Mount Arreat in the northern Barbarian Highlands.
As shown at the end of Act IV, while two of the Prime Evils of Hell, Diablo and Mephisto, have been killed and their Soulstones destroyed at the Hellforge, their surviving brother Baal has impersonated Tyrael and retrieved his own Soulstone from the narrator Marius.
Baal has raised an army and attacked Mount Arreat, whose Barbarian inhabitants are tasked with defending the Worldstone.