The Ancient Gods picks up after the end of the main story in a time where, due to the Slayer's actions, the armies of heaven and hell have fallen out of balance. The demons have flooded in to overtake the weakened angelic realm, so the Slayer's been called in to clean up the mess.

Your war is not over… slaying the Khan Maykr left an imbalance of power that threatens all of creation. The legions of Hell have razed the heavens, threatening to expand their control across dimensions. With the aid of an old ally, battle your way back to Urdak and decide the fate of the cosmos. Your mission is now your own. Experience a new mission in your eternal fight against evil. Unleash your vengeance and face your greatest test as you march back to the Maykr’s realm. Defeat powerful new threats, restore order to the heavens and unearth the corruption that has thrown the universe into chaos.