After we fought the ghouls, the only place left to go was the final chamber, where Black Tooth (the goblin leader) hung out with dozens of barrels full of the plague-causing slime. With him were 5 goblin sacrifices clustered around Black Tooth and two bat handlers flanking the passageway we entered from. Black Tooth cast a zone of darkness around us so we couldn't see, which was supposed to leave us vulnerable to the bats.
Problem was that cfoofoo forgot to include bats, and so the bat handlers were pretty much useless and Aramil just had to move forward in order to bomb the sacrifices with magic. Droogh and Mahtan attacked one of the bat handlers, Anakha forced the other one into a corner with his halberd, and Rider moved forward to attack the boss. Black Tooth had some annoying spells - like a zone of cover for him and his goblins, and a hex that would do 3d6 damage if the person it affected moved at all while it was still active - but other than that and an annoyingly high fort save he wasn't much trouble. The bat handlers had pretty terrible rolls and didn't do much damage, and so Droogh and Mahtan moved forward to help fight the boss, allowing their handler to flee. Anakha spent pretty much the entire fight beating his handler to a pulp while the goblin couldn't land a single blow.
Before long it was all over. We found the cloak of contingency in the boss room, along with some gold. We also took a jarful of the slime so we could bring it to an alchemist. With any luck, they'll be able to develop a cure, especially since the king is one of those affected by the plague.