On their way back to Sigil from the Gray Waste, the companions were attacked by a legion of baatezu. Dharnon and Celeste fought bravely but were gravely wounded. The others, seeing no hope for victory or retreat, laid down their arms and surrendered. Rupert, Zauriel, and Auron were led down to the shores of the River Styx, where a grim, black ferryboat awaited. One of the devils paid the merrenoloth ferryman, and everybody climbed aboard.

Their journey down the River Styx took them 5 days, leaving only 2 weeks before the Four Doors would close for another 500 years.

The companions, surrounded by devils, watched in despair as they suddenly found themselves in the blasted, rock-strewn hellscape of Avernus, the first layer of the Nine Hells. Hideous red clouds covered the sky, from which the occasional meteor streaked before crashing into the blood-dusty plain. Ambient light continually swelled up from just below the horizon as though lit by a setting sun. The atmosphere reeked of brimstone and burning tar, and hot gusts of wind shrieked across the hellscape to scour the land below.

A massive iron structure loomed ahead, like a pair of docking arms straddling the River Styx and extending out over it. The ferryboat pulled up here, moored to the dock, and all the baatezu disembarked. The companions were taken to the dock manager, a devil covered in engine oil named Bazelsteen. Their weapons were thrown carelessly at their feet. It was evident the baatezu did not fear them at all.

Nobody could speak Infernal, so Bazelsteen had to communicate with his new slaves in broken Common. He explained to them that, if they helped him with his experiment, he would give them their weapons back and their freedom. It seemed like a deal too good to be true, so they agreed.

The legion of devils formed up on the plain away from the river, and after a while they marched away.

Bazelsteen took the companions to a rusty barge anchored on the River Styx near the dock. Hanging from the barge’s loading crane by a rusty chain was a 10-foot-diameter spherical diving bell made of greensteel and glass. Suction tubes protruded from the diving bell’s lower hemisphere like flimsy arms. Bazelsteen had built this experimental bathysphere to dredge the bottom of the river for silted souls. He needed to test it, but he was unwilling to risk his devils. So Rupert and Zauriel climbed inside. “Whichever of you sucks up the most silted souls gets a coin!” the devil said.

Auron attempted to operate the crane, but couldn’t figure it out. Bazelsteen shoved the aarakocra aside and did it himself, lowering Rupert and Zauriel down into the black, coagulated river.

After about 10 minutes of dredging, during which time Rupert and Zauriel actually started having fun, the dockyard was suddenly attacked by a tanar’ri raiding party! Bazelsteen left to go kick some demon ass, leaving the barge and its crane unattended. Auron stepped in to try to crank his two comrades up out of the water, but he accidentally dragged the bathysphere across the river bottom instead. A chasme buzzed down to engage him, its wings making a horrid droning sound that hurt his ears, and its proboscis stabbed into him like a spear. Auron disengaged, flying over to the pile of weapons on the dock, and grabbed his two swords. The chasme pursued him relentlessly.

Howling, cursing, screaming, frantic, the demons and devils fought each other on the docks. Tooth and claw, frothing mad with fanaticism and ancient feuds, the tanar’ri rent and slew and died.

Auron returned to the barge, finally managed to get the bathysphere to raise up out of the river, all the while defending himself desperately from the chasme. With the help of Rupert and Zauriel, he finally defeated his foe. And it appeared as though the baatezu had also won the day.

Bazelsteen flicked blood from his spear and thanked the adventurers for their aid. He asked how many souls they’d siphoned up, and Zauriel proudly declared that he got more than Rupert. Pleased by this, Bazelsteen flipped the paladin a coin and told them to take their weapons and get out of here. Rupert handed him a business card. Bazelsteen studied it, then asked if they were headed back to Sigil. He told them about a barmy little devil named Gadreel who lived up the river a ways, claiming to be an angel. Perhaps this Gadreel could help them get home.

And with that, the companions took their leave of the docks and headed into the red wastes, following along the river in search of this Gadreel. Mountains dotted the blood-dusty plain, which itself was littered with rocks of obsidian and quartz. Some of the rocks seemed to have tormented faces etched into them, or occasionally took the vague form of some berk caught in the stone. The wind howled, carrying with it the screaming and weeping of petitioners doomed to suffer for all eternity. Avernus’s combination of oppressive heat and supernatural malevolence weighed on the bodies and souls of the companions, who were eager to get out of this burning furnace of a plane as quickly as possible.

They passed by a road made of bones pressed into the ground like cobblestones, and a bridge of similar material that spanned over the river. Beyond that, Auron spied a deep chasm from which green light and smoke emanated. He detected a portal at the bottom. But nobody had any idea where this portal might lead. Zauriel, who felt more exhausted than he ever had in his life, suggested continuing on, and if this angel couldn’t help them, maybe they’d take their chances with the portal.

Along the way they were ambushed by a swarm of giant frogs that leaped out of the river. The companions made quick work of these fiendish creatures.

After a few more hours of walking, Rupert and Auron felt exhausted, too. Zauriel summoned his steed, Myerai, to carry him. The padding inside his plate armor was sopping wet, and he felt delirious from the heat.

Finally they noticed a cracked helm and a greatsword lying half buried in the mud by the river. A spherical stone set into the sword’s pommel still gleamed with cerulean radiance. Zauriel and Auron raced to the sword. But then a tiny spined devil flew out of the helm and accused them of stealing.

This was Gadreel, once a solar angel who came down to Avernus to defeat Tiamat. Gadreel was sorely beaten, and as punishment for his hubris, Tiamat turned him into his present form. Millennia of isolation unhinged his mind, so he argued with himself often while conversing with the adventurers.

To regain his true form, Gadreel said he must spill some of Tiamat’s blood on the ground of Avernus. Fighting Tiamat in his present form would be madness, but Gadreel learned that a dragonborn named Arkhan the Cruel carried some of Tiamat’s blood in a reliquary around his neck. Rupert gasped, for he had heard of this Arkhan before. Gadreel revealed that the “gem” glowing on the pommel of his old sword was in fact an orb of dragonkind — an item sure to be of interest to Arkhan. He urged the adventurers to trade the orb to Arkhan for the reliquary and then return here.

The companions were skeptical of the devil’s tale, but they did not have much else for options (Myerai wanted to stab him with her horn, but Zauriel convinced her to stand down), so they agreed to help him. Gadreel gave them directions to Arkhan’s Tower, but Zauriel convinced the little devil to come with them, so he hopped inside the paladin’s backpack. They brought the sword and helm with them, too. The sword itself was beautiful, adorned with gold and feather motifs, and its blade a gleaming blue steel.

A dark tower loomed on the horizon, its black spire rising hundreds of feet, its ramparts bristling with charred skulls and barbed chains. Circling above the tower’s peak was a great white dragon stained with ash and soot. As the companions got closer to the tower, they noticed figures shuffling atop its ramparts — hundreds of undead guards. The dragon roared and landed on the ground when the companions stopped before the tower gate. A tortollan emerged from the tower to meet the new arrivals. This was Krull, whose shell was carved with Draconic runes. He was flanked by half a dozen ghouls.

The Rupert explained that he and his associates had a present for Arkhan. Krull demanded to see it first, but Zauriel told him that it was for the dragonborn’s eyes alone. Perterbed, but convinced (and slightly impressed by this mortal’s audacity), Krull led the company to the Monument of Tiamat behind the tower.

A colossal dragon’s skull leaned against the mountainside, surrounded by bones the size of houses. Acrid smoke rose from the skull’s maw. A tunnel at the back of the skull led to Tiamat’s lair. Military tents were pitched among the bones outside, and parked next to them was a two-wheeled infernal war machine. Gathered around the tents were dozens of chattering, reptilian humanoids with gleaming swords, white scales, and white, leathery wings.

Arkhan the Cruel came out to meet these adventurers who’d brought him a gift. And indeed he was impressed with the orb of dragonkind. He gave up his reliquary in exchange for the orb, and the companions were free to go — easy as that.

After they were a comfortable distance from Arkhan’s Tower and the Monument of Tiamat, Zauriel dumped Gadreel from his backpack and gave him the reliquary. The spined devil smashed it on the ground, spilling the blood contained within. Moments later, he shed his fiendish skin and grew back into his true form, that of a lawful good solar. Laughing gleefully, Gadreel snatched his sword away from Auron and planeshifted everyone to a gate-town that would take them back to Sigil.

The party inquired about more compensation for helping him, but Gadreel told them to store up for themselves treasures in heaven. And with that, the angel departed.