The Boss got away

Next on the list of things to do, clear behind those big huge doors. We just defeated a bunch of Skaven, and have taken control of their doomwheel. A short rest and we are back at it. At the end of the hall, where the doomwheel emerged, are two 15 foot high, double 10 foot, metal banded doors. I decide to check to see if they're locked and listen. There is a gurgling sound, like that of a bubbling cauldron. They also have been boarded from behind, no doubt with the same thick wooden beams used to make the doors.
 
I suggest using the doomwheel to break them down. Friar Karl volunteers to drive.
 
Unfortunately, our strategy is none too quiet, but that could not be helped. They knew we were coming and were well prepared. Friar Karl crashing through the doors as we charge. I glimpsed a chaos mutated Tiefling who finishes casting a spell and vanishes. Oh look, he suimmon a Demon, a Glabrezu. This confirms to me Demon involvement in this process. Dispater will be none too please as well as the other leaders of the 9 Hells. Organized Chaos Lords, Demon support, this is bad news, even for the Lord of Dis.
 
Upon crashing through, another surprise. Way up high on the ceiling is a Yolchlol. Yochlol's are hand maidens of Lloth, the Demon Spider Queen. Are these random, or have all the Chaos Gods teamed up?!?!?!
 
The Yolchlol immediately casts the Domination spell on Rory. BAD FREAKING NEWS. It orders Rory to attack Friar Karl. Luckily, Karl uses the Doomwheel as cover. Unbeknownst to our enemies, Freya has already cast Greater Invisibility. The Glabrezu grabs Friar Karl in its meaty claw. Rory is still dominated and trying to attack him. Freya unleashes a slew of magic in the form of Eldritch Blasts and Scorching Rays. BBQ Demon anyone? All we need is sauce!
 
I see an opening and jump in the doomwheel. I have to drive through my party to get a shot at the Yolchlol. The blades of the doomwheel tear into Rory, Kemurial and Friar Karl. Not a big deal really, soldiers are there to mop up damage. It's their job. I turn the wheel to have the blades cut into the Glabrezu. It renders flesh from the Demon. I have never piloted one of these but I take my best efforts and start chasing down the Yochlol, firing bolts of lightening at it. I am not hitting, but I am forcing the Demon to scatter, move and take cover. He however is not happy with me targeting him taking 1/3 of my health with his Caustic Lash.
 
As if Dispater saw we needed his help, Rory breaks free of his Domination Spell. Gaining his faculties, of which there are not many, he calls out,
 
"Hey evewybothy, I am back"
 
Rory then sends the Glabrezu back to the Hells.
 
Freya uses Telekinesis to hold the Yochlol in lace on the floor. The party then cleans up the Yochlol and the battle is over. I hope Lloth appreciates us returning her handmaiden. It is unfortunate that the Tiefling escaped. We decide to search the cavern. Rory and I see the bubbling Cauldron filed with acid like material and I suggest to overturn it and pour the acid into the work area, destroying the machines and the doomwheel. Unfortunately, it also destroyed the wall next to Rory and I and it collapses on us. Took a moment to dig out but now we are really hurting as well. Falling rocks are not gentle.
 
Behind that wall we find a bountiful treasure. 40,000 gold pieces, +2 Plate, a +1 Lance of Lifestealing among other minor items. I guess a wallfall aint so bad afterall!
 
Finally, I get in on a big take! I have been managing with minimal magic for sooooo long. This should boost my performance.
 
The tunnel out if fraught with numerous traps. A floor say, several pits and acid and all easily avoided. Using the magics we found and the new found funds, we are able it improve our positions.
 
Now to find that damn tiefling and make him pay with his life!