The Dark Borough's Slave Conflict

The most handsomest, cunningest, winningest group of curious and concerned adventurers from Falder Fell (Olen'yi Roga, Dr. Quidel Blackmire, Tarnfolk Ildsson, Maljar Wolfheart, and the wizard Xavier) resumed their trek to seek after the terrible serpent released from the Elven ruins.
They began their travels by taking an old trail they had begun to explore previously, northward through the forest and along the mountain ridge.
They rested with Vemplexia for a night and set out at dawn, passing the cavern hidden below the waterfall they had explored on their last outing. Though they were heading toward ruins they had glimpsed to the North/North-West, they also stumbled upon a cavern and felt that it would not be a thorough search of discovery against their mysterious enemy if they did not probe this unexpected geological feature.
At the mouth of the cave they heard a curious din of indistinguishable murmurings of many languages in the distance. Sneaking inside, down a long corridor intentionally carved, they found two ogre guards flanking as sentries: Zunzun and Ogar. After speaking with them they were allowed to pass into the Dark’s Borough Black Market where they met Svirfneblin selling exotic mushrooms and foodstuffs, Dueragar selling magically honed weapons and armor, and Drow auctioning off captured goblin and kobold slaves.
The party was invited to fight in a gauntlet pit against monsters that the folks there spectated as entertainment but declined, electing instead to explore the market. They spoke with various groups of both merchants and customers. There, Olen learned from the Lizardfolk about the mystical snake that they were in search of: whose name is Sevith, or Deathvenom; A god-like entity who gave power to a group of humans that warred against the lizardfolk in exchange for power. Ultimately, it was believed to have been killed by the Elves of the forest, but perhaps was only captured and is in fact the same snake that these adventurers seek.
Maljar spoke with a group of Hobgoblins discovering a possible location leading toward Rexgar along the Wyvern Ridge, whom they are allied with as they attempt to expand into Galyeeha but have reached a stalemate fighting with the Twith Fane lizardfolk. They also mentioned a Vost Keep which Rexgar seems to answer to located somewhere in one of the forested areas north of the river bend.
Dr. Quidel, disturbed by the slaves, questioned the drow trying uncover a way to interrupt their operations. He discovered they sell mostly in this market and likely have greater ties to the Underdark in general (one entrance, discover by Xavier, to be in this very same tunnel, barred by a drow woman who alone may open the door and permits none to enter unless they have been vouched for by a person of standing in the underdark or have won the gauntlet).
Beyond this, Quidel learned the slave master had recently lost two personal slaves that fled East (a human man and woman) and had sent outriders to seek them for recapture. Armed with that knowledge, the party set out to rescue them first, if possible.
They camped and continued East to the ruins they had found previously where they discovered the Drow’s mounts and a camp. Inside, they roused Drow who were sleeping through the day hours, awaiting a departure during nightfall with their successfully recaptured slaves. The two groups fought bitterly, the doctor nearing death twice, but ultimately the slavers were thwarted.
The man and woman were set free and offered nourishment and medical attention. They were given the choice to return with the group to safety in Falder Fell and currently reside in olen’s quarters while they attempt to recover and begin their life of freedom anew.