This will be a quick summary.
The Odd Three, having returned from their last adventure, are home at the Inn of the Eye. They open the portable hole to retrieve some of their loot. A 6″ tall red Pillsbury Doughboy looking creature jumps from the whole and lands on top of a shelf in Debi’s room. It fights them, throwing strong fire blasts at them and causing fires wherever the shots miss. It fleas down the hall and they pursue. It continues fighting them as it grows to about 8′ in height. They manage to kill it, but there are fires burning all over. Debi uses Prestidigitation to put out the fires.
The next day they are served with eviction notices. The Odd Three have a week to find a new place to live.
They find out that the old Orelli house, in the Merchant District is for sale. Research reveals that its owner, the recently deceased Mortaz Orelli, was some kind of magic user, and the house is shunned. His family, once popular and prosperous has fallen into decay and is also shunned. They approach his nephew, Stephan Orelli, the executor of the estate, about buying the house. He offers to simply GIVE them the house if they will retrieve one family heirloom from it, the Orb of Orelli, a small crystal ball on a fine silver stand. They agree.
The Odd Three find the house is enchanted against “Good”. They find a weird portal in back yard. They detect magic inside the house. They explore the house and find it to be very fancy. There is a lounge that appears to be designed for oratory or performances. As they go to the second floor, Skargg (who is with them) is hit by a crossbow bolt booby trap. He survives. As they explore the upper floor they fight 3 shadow demons. They find a portal to what seems to be a basement. A Quasit familiar takes the Orb and flees through the portal. They follow it, kill it, and fight a Horned Demon. They are doing damage, but it is very very tough. Finally, Debi casts a spell and it fails a Fear saving throw and flees through the portal to hell it came from. Simon dispels that portal. The retrieve the Orb.
Stephan Orelli is good to his word. The house is theirs. They call in some favors from Abbot Lightman of the Akki Temple and from their ally Abbot Mouseman, of the Temple of the Rat God. Together with them, they manage to “disinfect” the house.
Debi discovers a book about the portal in the basement. Turns out the basement is not actually under the house. The portal goes to a chamber far from the house, deep in the ground. They find out how to open the massive steampunk circular gate to the Undercity, as well as Mortaz’s journal describing his pacts with the underground human society accessible via that gate and the Kuo-Toa civilization, that is far underground and outside the city walls. They consider if they should explore and make their own pacts, by which the humans and Kuo-Toa will be at peace with each other and guard that part of the Undercity from intruders who could try to enter the “basement” and thus the house.