From the WotC plot recap:
"Bane's power knows no borders." Or so his servants claim. It is a frightening thought. The Lord of Tyrants seeks to extend his dominion over the Delimbiyr Vale and the caverns below; and, as we found out, over both the living and the dead.
- - Teseryne Truesilver
- - Daughter of Talanthe Truesilver
- - Year of Rogue Dragons
The call came again in the middle of the night. Lisyil Sweetwhisper awoke the members of the Jade Blade to inform them that High Lord Kalahar Twohands wished to see them immediately. Quickly dressing, the adventurers hurried to the High Lord's Hall to find out what was so pressing.
Kalahar received another dream from Mielikki. The Jade Blade's earlier experience in the Heart of Bane, in the Fortress of the Eternal Despot, caused another premonition from the Lady of the Forests. A great evil was hidden in that place, but the details from the dream were flitting away from Kalahar.
Chancellor Vendross Thaddren had uncovered information about the Heart of Bane. The fane housed phylacteries of those who died fighting against the Dark God. Each black crystal had a soul trapped within it. As if this was not bad enough, Vendross's research revealed that a chamber beneath the Heart of Bane housed an evil artifact called the Scepter of Eternal Dominion, which holds power over souls who died in opposition to Bane. Vendross cautioned that a watery death waited any who sought to recover the scepter.
Kalahar wanted this tool of the Banites removed for the safety of both Loudwater and all that was good in the Delimbiyr Vale, so he asked the Jade Blade to return to Orlbar and retrieve the scepter. He also wanted our heroes to avoid a watery death, so he gave the adventurers potions of water breathing to help them on their quest.
The Jade Blade journeyed back to Orlbar and the Fortress of the Eternal Despot. Once again, they opted to use the culvert to get inside the temple. But this time the Zhentarim had taken steps to prevent access, trapping it with a powerful spell. The adventurers were a trifle incautious and set off the trap, which summoned a pillar of flame down onto them, burning some of them badly.
The rest of the crawl through the culvert was uneventful and they found themselves in the Heart of Bane shortly thereafter. No sooner had they stepped out onto the bone walkway when they were accosted by two priests of Bane—the Tyrants Venrik and Greaves. The bone walkways helped the priests by lifting them from one walkway to the next while ripping and tearing at the adventurers. The tyrants summoned fiendish monsters to aid them, then cloaked themselves in mist before joining the fight. The battle was confusing as the priests constantly moved about thanks to the walkways; but the Jade Blade eventually killed them.
With the deaths of the two tyrants, the Jade Blade could explore the Heart of Bane at their leisure. They found a secret door that opened to a spiral stairway leading down to a vast cavern dominated by a lake. On the narrow shore they found a marker with the clenched fist symbol of Bane and words written in the tongue of fiends. It read "Bane's dominion knows no border".
The Jade Blade drank their potions and dove into the lake. The murky water made it difficult to see, but at the very bottom they found a hole in the lakebed. Next to it was another marker with the symbol of Bane. It was written with the words "Hatred is the path to power. Tyranny is the way to rule." Regrettably, the marker was trapped and touching it unleashed another blast of infernal power on our heroes.
The hole led to the Sunken Temple of Bane. It was flooded, dark, and deserted. The adventurers explored the water-filled passages, which were decorated with murals depicting worshipers of Bane as well as strange human-fish crossbreeds emerging from a portal to greet the worshipers. While they swam through the halls, they were attacked by a water elemental and by restless, mad spirits of tyrants of Bane who had become allips. In addition, they were attacked by a school of the human-fish crossbreeds that I have recently learned are called scum. They fought off all these threats and delved deeper into the temple.
The Scepter of Eternal Dominion was hidden in the last and largest chamber of the Sunken Temple, called the Hall of Devotion. Floating in the water over the large stone altar that was obviously used for sacrifice was a primeval fish-like monster called an aboleth. The horrid thing reached out with its mind and seized control of two of the Jade Blade, forcing them to attack their companions. Our heroes reacted swiftly and countered the compulsion with a ward that protected the enslaved adventures from evil and prevented the aboleth from exerting control. With its most fearsome power neutralized, the aboleth did not last long against the vengeful blades of our heroes.
With its last ounce of malice and strength, the aboleth knocked over the sole pillar that held the hall's roof up. Without the support, the Hall of Devotion started to collapse in on itself. As the pieces fell away, the adventurers noticed a hole in the roof that led up and out into the River Greyflow that flowed above them. The Jade Blade desperately searched for the scepter, which they found hidden beneath the altar. Their prize in hand, the Jade Blade swam out of the collapsing hall into the river and finally to the surface and fresh air.
The Jade Blade made their way back to Loudwater where they turned the scepter over to High Lord Kalahar and Vendross Thaddren. Kalahar was quite pleased and instructed Vendross to secure the scepter so that it would not fall into Banite hands. The High Lord thanked the Jade Blade for their service and rewarded them handsomely.