Here's the intro I came up with. The opening portion with Sheila Heidmarch is my own, but the parts in Kaer Maga borrow heavily from the other threads linked above and the module itself.
“As you probably know, the city of Kaer Maga is located at the top of a cliff in eastern Varisia. The cliff side itself is the site of many enormous statues, remnants of the Thassilonian Empire. The mouth of one of those giant statues, revered as possibly some long forgotten god, is the entrance to the Godsmouth Ossuary. For those who live and die in Kaer Maga, this is the most prestigious, and expensive, place to be buried.”
“Obviously, the ancient nature of that site makes it an exciting prospect for exploration by any archaeologists, our Society included. We’ve long suspected that there might be exciting remnants of ancient Thassilon in those passages below the city, waiting to be discovered. But the site is controlled by the church of Pharasma, who restrict entrance to the ossuary quite strictly. Not even mourners are allowed to enter. Only the priests and those dead they bring to entomb are allowed entrance.”
“I’ve contacted the church of Pharasma in Kaer Maga several times, hoping to gain access, but I’ve always been rebuffed… until now. Just this morning, I received a message from one of their priests, asking for the Society’s help. If I send a team of Pathfinder agents to help them with a problem, they’ll allow that team to explore inside the Godsmouth.”
“So I’m sending you to Kaer Maga. You will meet with a priestess named Valanthe Nerissia in the Godsmouth Cathedral, and follow her instructions precisely. Whatever task they need our help with, you will do. And then you will explore whatever areas of the Godsmouth Ossuary that they allow. If the priests put restrictions on how deep you may explore, don’t disobey their instructions to venture outside those bounds. Maintaining a good relationship with the church is essential. I’m hoping to be invited back for more exploration later.”
“Are there any questions?”
Once the Pathfinders are done asking questions, Venture-Captain Heidmarch calls for an elderly wizard to enter the room. He barely looks at the Pathfinders while casting the spell to teleport them directly to Kaer Maga, the City of Strangers.
Once there, you make your way through the labyrinth-like multi-storied streets to the southeast section of the city, known to locals as The Bottoms. The gothic majesty of the Godsmouth Cathedral towers above as you make your way down a gravel path to the front doors of the church. To the north, thornless black roses, thought to bring good luck, are planted in a bed in the center of the path, while to the south, rowan trees provide homes to sacred whippoorwills, birds believed to guide departed souls to the Goddess Pharasma’s otherworldly sanctuary known as The Boneyard. The two knockers on the double-door to the Nave are carved into large silver spirals.
A priest wearing dark purple and midnight blue robes answers the door and leads you to a private room inside the cathedral. He asks you to wait while he notifies Cryptmistress Nerissia that you have arrived.
A few minutes pass and the priest returns, accompanied by a somber woman dressed in dark purple and black robes. Her gray hair is streaked with silver and is pulled back into a bun. She looks you over as she approaches and then gives a curt bow to the group. The other priest leaves, closing the door behind him.
“Welcome to Godsmouth Cathedral. I am Cryptmisstress Valanthe Nerissia. Your Venture Captain assured me that you could help us resolve our problem.”
“Over the last month, bodies have gone missing from the lowest level of our Ossuary and we need adventuring sorts such as you to investigate and, if possible, put a stop to the disappearances. Many noble families invest their fortunes to see that their loved ones are kept safely at rest in the catacombs of our Ossuary. It would be an embarrassment, to say the least, if this information was leaked to the public, so your discretion is most appreciated.”
“You’ll be going down into the lowest level of the Ossuary, which hasn’t been used in decades, possibly centuries. Besides investigating the disappearances of the bodies, we’d also like you to clear that level of any monsters or other threats. You are permitted to keep any valuables you find so long as they do not belong to the deceased entombed within. Any Pharasmin relics should be returned to me so that they can be given their proper reverence in our library and temple.”
Before going down to the Ossuary, the priestess gives you the opportunity to journey out into Kaer Maga to buy any additional equipment, and prepare yourselves properly. She once again urges you not to repeat any of what she’s told you.
When the PCs are ready to begin, Valanthe meets them and leads them down the narrow, twisting cliffside path to the Godsmouth Ossuary. Once they pass through the mouth of the Unnamed King, they are in the ossuary proper, where robed and hooded Pharasmin priests quietly tend to the deceased. Valanthe leads the PCs through luxuriously appointed catacombs packed with bodies and down several stairways before coming to an area that obviously sees little use—most of the burial niches are empty and dusty, the air is musty and close, and silence reigns supreme.
In this disused portion of the crypts, Valanthe stops before a locked door. She explains that this is the only known entrance to the sealed lower portions of the ossuary, and once you enter, the door will be locked behind you. Because of this restriction, you will be unable to leave the ossuary to rest and resupply between encounters. To help you accomplish your task, Valanthe gives each of you a potion of cure light wounds and a vial of holy water.
Valanthe then hands you a hollow mithral tube about 1 foot long—a chime of opening with 5 charges remaining. You may use the chime to get through the Pharasmin seals below, but you should make sure you save at least 1 charge to get through this door again on your way out— the priests will not open the door for you if you don’t have the chime, as they have no way of seeing through the locked door to recognize you or determine whether something has turned you into mindless undead. If you lose the chime or use up its magic, you must find their own way out of the ossuary. With this warning given, Valanthe draws a large iron key from beneath her robes and unlocks the door. The Godsmouth Ossuary awaits.