Everyone, including the drow, squeezed inside the mobile stronghold. Following Tierak's directions, Bolias tunneled down to the lowest level of the city, formerly the home of House Morcane.
As they tunneled through the rock, Clicker buffed everyone up by casting mass conviction, mass shield of faith and recitation. The stronghold could only tunnel through unworked stone, so Garyn used his staff of transmutation to disintegrate the masonry walls of House Morcane. Elsa drank a potion of spider climb and she and Rohit found themselves in a short corridoor, 20ft wide, with a door at each end. When they set foot inside, they were damaged by the forbiddance spell that was in effect. Also, the purge invisibility that was tied to the unhallow spell made both of them visible.
Lukwind began his bardic music with inspirational boost and climbed out of the stronghold as well. Garyn climbed after him and Martok flew out. Rohit could hear somebody spellcasting, behind one of the doors. Clicker attempted to use his ring of blinking to phase through the rock into the corridor, but the forbiddance prevented it. Martok asked Rohit, "Do you really think it's worth searching that door for traps?"
"No, probably not," Rohit replied. "In my professional opinion, there's no way they would trap this door." He pushed it open and jumped aside, just in time to avoid a glyph of warding. Elsa, who was standing beside him, was slightly singed. Garyn and Lukwind failed their saves against the symbol of weakness and were both paralyzed. Inside the doorway, a hovering skull emitted a piercing shriek that could be heard up to a quarter mile away, deafening Lukwind. Martok destroyed the skull with a vitriolic blast and chained to a gaunt woman who was reclining atop a pedestal in the center of the room. She didn't even flinch, which led Martok to believe that she was an illusion.
Elsa charged into the room to attack the woman, but wasn't able to hit her. However, she was able to use her mind over magic ability to reflect the destruction spell that was aimed at her. She was then able to see through the illusion, as was Rohit, who had heard Dorina T'sarran casting the spell. Rohit and Elsa flanked the vampiric priestess while Martok fired another vitriolic blast. Rohit was able to deal considerable damage with his deathstrike bracers, but Elsa's powerful blows were turned aside by Dorina's iron bones.
Dorina conjured a blade barrier across the doorway, but another backstab from Rohit and vitriolic blast from Martok dropped her to 0 hit points and she turned to vapor. Rohit and Elsa watched as the gaseous form of the priestess evaporated into the wall. Rohit found a secret door, but couldn't determine the mechanism to open it. Elsa brandished her qullan greatsword and set to work chopping it down.
Meanwhile, Helena had flown out of the stronghold to drag the paralyzed Lukwind back to the platform of healing. Martok grabbed Garyn and did the same. Tierak Morcane and her drow were searching the other rooms, but hadn't found anyone. Clicker explored further down the corridor and heard two voices casting spells. He hid in a doorway and soon enough one of the vampire noble guards showed himself. Clicker shot him with a scorching ray, but then retreated from the vampire driders who followed. The drow allies opened fire with their hand crossbows, but were unable to injure the vampires. Tierak gave the order to retreat.
When the vampire noble guard stepped around the corner, he was simultaneously shot by Clicker, Martok and Garyn. He instantly turned gaseous and floated away. One of the driders charged forward and grabbed one of the drow allies in its claws, sinking in its fangs and draining her blood. However, once again Martok and Garyn make short work of it. It, too, turned gaseous. The other drider decided against coming around the corner, and retreated instead.
When Elsa broke down the door to the treasury, she found it empty save for an ornate sarcophagus. Rohit searched and disabled the trap, then the two of them dragged it across the floor, back to the mobile stronghold. Lukwind said that he would take Dorina's body to the surface, where it could be exposed to the sunlight. He also took the body of the drow who had been drained by the drider, just in case. He estimated that he would be back in two minutes.
The rest of the party and the drow headed down the corridor to search for the coffins of the other vampires. When Clicker stepped around the corner he was shot by several crossbow bolts, but was able to resist the sleeping poison. The drider was standing in the middle of a temple, accompanied by two more vampire nobles and four quth-maren. Martok fired his vitriolic chain and Garyn shot silver, undead bane arrows. Clicker and the drow charged into the room to engage the undead in melee. One of the drow was killed and Clicker suffered an energy drain attack, but it only took a few short seconds before the quth-maren were destroyed and the vampires had turned to vapor.
There were two enormous webs in corners of the ceiling, where the vaporised driders had fled. The vampire nobles fled through a door in gaseous form.