The only hint given to the players was the title of the adventure: "Whistles in the Dark."
The PCs arrive at Plane-atary Express to find a flyer/note on their door inviting them to a performance at the Weary Head in the Hive. The Weary Head is a well known Bleak-nick bar where the artistic Bleakers gather and share their poetry and other forms of performance art. The flyer/note was signed H. H., which Bobby took to be some kind of salutation ("Hi Hommies!"). It is actually the signature of the advertiser Harys Hatchis (Uncaged: Faces of Sigil). Also, at the bottom of the flyer was a hand written note asking the PCs to meet with Jorun regarding a possible job opportunity.
When the PCs arrived at the Weary Head, the fensir twins Morvun and Phineas were performing (Uncaged: Faces of Sigil). This gave me the great opportunity to read some of Morvun's death "poems" which was really fun. Also, the art of the duo was really fun to show the players. During the performance, the PCs took up seats at the bar and hunted around for their contact.
After a few drinks and a little asking around, Jorun approached the group and informed them of the job. He wanted the PCs to go to the Slags and retrieve a tanar'ri supply cache. After that, he wanted them to take the cache to the town of Windglum in Pandemonium. Their, they'd get the portal key to come home and he'd pay them 2000 GP each and that they could find him at the House of the Griffen (Factol's Manifesto). The Slags are the most dangerous and decrepit part of the Hive where many crazy monsters wander around and no shops are set up (In the Cage: A Guide to Sigil).
The PCs agreed to the job and went off to hire some muscle to help them get through whatever they might encounter in the Slags. Hiring a group of four dwarves, the group headed into the Slags. While following the directions to the supply cache, Nearin was almost sucked into an ooze portal. Ooze portals are randomly appearing one-way portals between Sigil and the Para-Elemental Plane of Ooze, and the hands of ooze mephits have been known to grab at anyone walking by (In the Cage: A Guide to Sigil). As Nearin and one of the dwarves struggled with the ooze portal, a group of ooze mephits hovered into view from behind some collapsed buildings. A brief fight ensued with most of the players and dwarves fighting off the mephits while Nearn and a Dwarf struggled to pull themselves free.
After the fight, the PCs continued on to the supply cache. While approaching the cache, the PCs were struck by the strong smell of cinnamon. Also, near the cache itself there was a macabre scene of tiefling bones spread about in almost some kind of artistic manner. These were signs that the Kadyx had passed by recently (In the Cage: A Guide to Sigil). The cache itself was a small, human portable, sealed silver crate.
The portal to Pandemonium was two fallen columns just at the edge of the slags and the key was a bell without a clacker.
Entering into the Pandemonium layer of Phlegethon, the PCs stood at the entrance to a large cave. Deeper in the cave was the anthill of Windglum, a town of barmy people who had spent too much time in Pandemonium. Entering into the town, I described a few of the inhabitants and their various insanities. After that, I gave description over to the players to describe the behavior of an inhabitant.
At the Scaly Dog Inn, the PCs sat down and ordered a round of ales. While most of the patrons were sitting alone and muttering to themselves, a small group of bashers were sitting around a table scheming. The PCs, sitting near them, started dropping hints about why they were there and that they were looking for Kadin. Eventually, the other table noticed and ask the PCs to follow them to a back room.
In the back room, the leader of the three barmy bashers started demanding who they PCs were, why they were there, and who told them to come. The PCs tried being evasive for a while and eventually spilled the beans about who had hired them. The leader then took the box and had one of his cronies tell the PCs about the key to get back to Sigil. The key was a whistle that when blown produced no noise. The whole group of thugs was saying stuff about silence and luck the entire time, which the PCs didn't really pick up on.
After getting the key the PCs rushed to the portal and quickly tried to activate the key and portal. Turned out the Anarchists (Revolutionary League, this was obvious at this point) had tricked the PCs and given them wrong information! They were transported to some other part of Pandemonium and were surrounded in darkness.
While standing about in one of the many tubes that make up Pandemonium's second layer, the PCs were battered by a terrible wind and had to make checks versus "Wind Madness" (Planes of Chaos). Everyone passed the first round. When the winds finally died down, the PCs heard a terrible series of cries coming from their left. One of the voices was very high pitched with a stutter and the other was very low pitched punctuated with grunts. The voices were talking to each other, calling each other Cat (high voice) and Bru (low voice).
The PCs discerned that the two figures had decided to split up, with Bru heading towards the PCs. All the PCs have infravision, so they were able to see Bru the moment he got close. He was a cambion who had been blinded and was missing his eyes. The PCs sprung into action and tied up Bru, though he was able to get one cry off before he was subdued.
After a few second, Cat appeared on the ceiling. Because of the gravity in Pandemonium is screwy, it is always in the direction of your "feet". This meant that Cat, a blinded and sicked Beholder (!!!), was able to float over the heads of the PCs at shoot off an eye beam before they could react.
The fight was really intense and the PCs made good use of the gravity to aways have the wind to their advantage. Also, Cat was missing 3 of its eye stalks, which made their lives a little easier. Kale, Norbys, and Bobby were fighting valiantly but were racking up damage really fast. Nearin was able to shape change into an arcanoloth and scare off Cat by threatening it with an army of yugoloths.
After the fight, the PCs questioned Bru for a way home. Bru, in a show of good faith so they wouldn't kill him, showed them a stash of dead adventurers gear. Inside was a bunch of magical weapons and some gems stones, which the PCs happily took. At this point, I had the PCs make saves against Wind Madness again, which Nearin and Bobby failed. The first stage of wind madness is anger, which manifests as impatience and violent behavior. They kept threatening Bru the entire time. The items were a +1/+3 vs Chaos long sword, and 3 +1 daggers that were unaffected by wind.
Eventually, Bru told them that at the end of this tube was a bottemless pit called the "Screaming Pit" which the winds whip out of at incredible speeds. Apparently this could act as a portal back to Sigil if the user was able to accurately picture an image of pure silence. Bru couldn't use it because he had gone far too mad while living in Pandemonium.
At the edge of the Screaming Pit, I had the PCs make one last save versus Wind Madness. Norbys, Bobby, and Nearin all failed. Norbys went to stage one and got super impatient, while Bobby and Nearin entered the apathy stage where they were unable to motivate themselves. Norbys then, a person who believes their is not point to it all, had to convince the others to jump with him. This was an absolutely hilarious RP moment.
The PCs landed in the Market Ward, falling through the portal made up of a stall's canopy and on to a seller's apples. Back in Sigil, all the effects of Wind Madness stopped, and can only return on Pandemonium. The PCs were over joyed to be back home. They took a short rest then went to hunt down Jorun at the House of the Griffen, hiring the same dwarves again.
At the House of the Griffen, they tracked down Jorun and took him out back. Their the dwarves gave him the boots, medium style, until he finally agreed to pay the PCs more than he had initially said he would and that he would leave them alone forever. Jorun had initially planned on not paying the PCs as they were expected to die in Pandemonium. Jorun then led the PCs into the secret back room of the House of the Griffen and into his Anarchist cell's hideout. There he gave them the 2000gp and an additional 200gp for them to keep quiet.
The PCs then got a magical message from Balial that he had a surprise for them. Returning to Planeatary Express, Balial revealed that because the PCs were so good at their job he was going to take them on a week long vacation to Sylvania, the gate town that is always partying!
I wrote this adventure and I am decently proud of it. The obviously weakest part of the whole thing was the portal key deception in Windglum. It was generally the most railroaded thing I've done in a while, but the players were kind and went along with it, though, which helped. This adventure was also a real GMing landmark for me because for the first time in the 12+ years I've been playing, I felt I had run a completely engaging and interesting session. I was glowing for days.
The energy throughout the whole adventure was good. The players reactions to Wind Madness were priceless. The fact that getting home relied on an impatient Bleaker giving a pep talk to a depressed and uninterested Cipher and Sensate was incredible. It is still talked about weeks later.
Another really fun part of the whole adventure was that the players were able to actually fight a beholder, albeit a weakened and insane one. Beholders aren't the kind of monster you face on a regular basis, if at all, because they are too "classic" D&D. What better venue to encounter one than in Planescape?! One of the players even tweeted about it, which just about made my day.