In the aftermath of Demogorgon and Eiber’s defeat, Althaea begins the laborious process of refinishing the layer of the Abyss in reduced horrific decor. She meets her new advisor, the obnoxious and egotistical quasit Gazbordical. Content with the idea she’s made the plane a better place after observing a unicorn foal settling in, the group sets off to meet with Hamanu’s troops at the Red Obelisk.
Their army is daunting, composed of thousands of troops including elite Urikite soldiers, Xanthusine devil hunters, a grove of Druid acolytes, cultists of Althaea, Thri-Kreen clansmen, gladiators loosed from the slave pits, and even constructs built by the inventor Kwalish who rides a massive construct of his own.
Samm issues a rousing war speech and gets the troops fired up, though he falls to heat exhaustion when drilling with soldiers literally several days straight. He rises from his chair on the final day before the attack in good health, raising the morale of the troops, and Hamanu opens the portal to Hell that they will march through.
They arrive on the other side in an absolute maelstrom of swirling blades, hellfire, and infernal bodies. Hamanu orders the assault on the high ground, to leverage the army’s siege engines and wizards most effectively. The group eliminates the horde of devils defending a guard tower on a nearby hill, cutting down hundreds as they push through the crowd and claim it for the army’s heavy hitters.
They then engage on a campaign of war that takes several weeks, advancing across the ruinous terrain of Avernus, the first layer of the plane of Hell. Casualties are great as they wage this campaign, but the heroes persevere in spite of it and some warriors make it all the way to the mighty plug between the layers of Avernus and Dis, guarded by the finest of Hell’s warriors the devil lord Bel.
The fight with Bel is incredibly dangerous, and many of the surviving warriors are cut down either by Bel’s minions or his mighty flaming greatsword. In the end, the most surprising cost is the life of Althaea, who is beheaded by his infernal blade. However, Samm and his allies are able to claim vengeance, killing the general of Avernus and laying claim to Hell’s outermost layer.