Given input from my players, I am trying some sort of hybrid campaign that borrows flavor from Serpent's Skull, Carrion Crown, and (I have since realized) Second Darkness. Possibly more. I am developing the skeleton of a plot, here - I'll be putting meat on the bones later, so I don't need specific encounters or descriptions. Mostly what I am looking for is critique on viability, and ideas for factions/locations/existing NPCs. The adventure will start at level 1. I will not be using experience points - my players will level when I think they have reached an appropriate plot point, and encounters will be tailored to this. (Treasure control will be needed because of this, of course.)
The party begins on a quest to find a lost archaeologist at an Osirion dig site. Clues at the site point them towards a lost civilization deep in the Mwangi expanse, that had a power based on the starmetal abysium. However, it also destroyed them in the end when insane deities (Great Old Ones) cursed them. The party will find that the archaeologist (and his encoded notes) came to the attention of the Night Heralds, who drooled over the whole legend, and the possibility of of riches in the form of feverstone.
Meanwhile, an Ustalavian nobleman (vampire!) has come to Osirion looking for the archaeologist, because he thinks the man might have info from a previous dig useful to him. Probably something involving the Whispering Way. Anyway, he finds out about the lost culture as well, and has his minions go looking for the lost civilization.
At this point, there are now at least three factions about to go racing after this lost civilization - the Whispering Way (thanks to the vampire), the Night Heralds (who have the archaeologist and his notes), and the party. If the party doesn't keep their mouth shut, there may be more groups forthcoming.
The legends, of course, are true - after a long journey, following several clues and during which the archeologist's notes are recovered (but not the archaeologist himself) the lost city is discovered. (Yes, this middle needs work.) Inhabiting it are alien monsters (mutated akata and more) and undead (ancient tribal warriors) by the plenty. The heart of the city contains the mine where the people got their abysium, as well as some of the things they built from it - including a gate, which is where the Great Old Ones came into the picture. There is also evidence that they were trying to call on the Great Old Ones because they were fighting something already, from underground. Stupid players at this point could try to activate the gate, and Hilarity Would Ensue. Or actually, not, as the gate has parts missing. Good thing, as the Night Heralds are already there, and would have definitely turned it on. And the Whispering Way isn't far behind. The party rescues the archaeologist at this point, but finds that the NH cultists have gone into the mine to find the missing bits - in short, if the party doesn't act, they'll open the gate and Bad Things Will Happen. The archaeologist refuses to enter the mine. Kinda sucks for him, because while the party is down there, the Whispering Way gets to him. And of course, they now want to go into the mine, too. (Actually, the party might be able to ally with them. After all, vampires and liches don't want to rule a world full of alien horrors eating their food supply and research subjects.)
At first the mine is more of the same as the city, only worse. But it soon turns out that it leads DEEP down - as in, apparently the ancient civilization got their abysium as remnants from the path of a fallen rock that punched into a previously unknown Orvean Vault. In the Darklands. Luckily for them, it caused rockfalls in Sekamina and the Vault itself to seal off the area. Unluckily for them, they weren't content with the remnants and dug through anyhow. This is where they unleashed some Orvean horror - or maybe it was something brought to the Vault by the rock and then sealed away. Either way, they tried to save their civilization by calling on the powers of Abysium, found the Old Ones, and got "assisted" by being turned into monsters themselves.
So now the players have to travel down to Orv, stop the Night Heralds from activating the gate again, and probably stop the Whispering Way too.
It seems a bit busy, but if you think of it as an AP, with separate yet connected adventures, I think it could work. However, this would basically only be the first adventure and the last two. I still need ideas for parts 2 through 4.