Act III - The Infernal Gate - takes place in the deep jungles of Kurast from being swallowed by an aggressive jungle, but also try to catch up with the Dark Wanderer and stop him from reaching Mephisto., and the hero needs not only saving what little is left of
The hero arrives in Kurast Docks, one part of Kurast that has not yet succumbed to the magically malevolent jungle, trying to swallow the whole city. Our protagonist arrives on a boat with Mashif, who is totally shattered when he see what has happened to his homeland, asking the player to save the city from the Jungle-plague.
Continuing towards the original plan for traveling to Kurast, to stop the Dark Wanderer, the player seeks relics of the former , Khalim, in order to create an artefact known as Khalim's Will that will be able to destroy the Compelling Orb preventing entry to Mephisto's domain, as well as corrupting the priesthood.
Town alchemist, Alkor contacts the hero, explaining he could possibly foresee the future of this demonic invasion if he can get the Black Book Lam Esen's Tome. When the player finds this, Alkor can reveal the Jungle Plague's source comes from the , primarily from Mephisto.
Then Ormus intervenes and gives the player the quest to destroy the High Council of Zakarum at Travincal. During the course of the quest, the player uses Khalim's Will to destroy the Compelling Orb and reveal Mephisto's secret lair.
The Lord of Hatred himself is then confronted in an epic battle that frees the people of Kurast from the Jungle and allows the player to enter the Burning Hells.