At the end of Diablo II: Lord of Destruction, players defeated Baal, but not before the Lord of Destruction corrupted the Worldstone at Mount Arreat. Originally, the demon Lilith and the angel Inarius used the Worldstone to create the world of Sanctuary and protect their new world from the invasion of Heaven and Hell. Additionally, the Worldstone had the ability to dampen the power of mankind preventing them from becoming more powerful than angels and demons. While it's speculated that the Greater Evils wanted to corrupt the Worldstone in order to invade Sanctuary en masse or even to subjugate mankind to their will, Baal's corruption of the sacred Worldstone did not bode well for Sanctuary and its mortal inhabitants. As such, Tyrael, Archangel of Justice, shattered the Worldstone with his blade Eldruin in an attempt to thwart the Greater Evils' plans.
Now 5 years after the destruction of the Worldstone, the Archangel Tyrael is presumed dead, and mankind is left to deal with the aftermath of his actions. Mount Arreat is nothing but a crater and scattered fragments of the corrupted Worldstone taint the land, bringing forth ancient evils who are looking to harvest the stone’s power and use it to control humanity.
The demon known as Skarn, Herald of Terror—once Diablo’s most powerful lieutenant—is rallying a new demonic army. Skarn intends to gather the fragments of the corrupted Worldstone and use them to resurrect Diablo, reigniting the Eternal Conflict between angels and demons. Players will race against the forces of Hell to find and destroy the Worldstone fragments before they can be used against mankind.