Big spoilery story behind the spoiler…
[spoiler]When 3.0 came out, I ran the premade module series that gets the characters from level 1 to 20. In the final module, the characters learn that an ancient dragon, whose heart was removed, managed to survive the experience by grabbing a demon and jamming it into the cavity left behind by the missing heart. This was only moderately successful and the dragon can only live by feasting on the souls of unborn children, resulting in children being born without souls.
In the D&D world, being born without a soul seems to mean being born without any initiative (no jokes), no drive, no verve or lust for life, no desire… people began to notice that some of the children being born were listless and quiet, and (given that they were newborns and couldn’t speak) gave the impression of being brain-dead.
Where the unborn souls are supposed to reside is called the Well of Souls. That’s where the dragon is hanging out, snagging the occasional soul and eating it. The task for Our Heroes is to go there and convince him to Stop That, with a certain amount of Dragon Death involved.
Problem: The gods themselves are, on pain of being made Not Gods and very likely Not Alive, absolutely forbidden to speak about the Well of Souls. In any way possible. The only source of information available to the party is to follow a trail of breadcrumbs left behind by people who had researched this in other ways. The party COULD NOT use any divinatory magic. Well, they could, but they wouldn’t get answers. They had to trust people purely on face value (and divination about those people? No answer). My players had a problem accepting anything at face value; they always assumed it was a trap.
So all of these parents notice their newborn babies are nearly lifeless. They go to the priest to find out what’s wrong. The priest casts a few spells. No answer. Huh. The priest goes to a higher-up and requests the boon of higher-level divination. No answer. Huh. Without telling anybody, a really-high-level cleric goes to the Plane of the Gods, finds his god and asks the god to her face what’s going on. No. Answer.
Children are being born without souls and the gods themselves are unable or unwilling to say why. Mass chaos and panic are literally going to ensue at any moment. And what are Our Heroes doing?
Well, about ten levels ago, they got a pair of Boots of Teleportation, which allowed 3 teleports a day. They then adopted the 15 minute workday in grand style… they’d teleport to wherever they were adventuring, get into a huge battle that wiped out all their resources, grab all the loot, and teleport back to town to rest up overnight and sell all the loot. They were teleporting anywhere, any time. At this point in the campaign, they now had access to many multiple Teleports per day as well as Teleport Without Error, and no power in the universe seemed capable of stopping them from bipping around like spastic blink dogs.
Except random encounters, apparently. See, somebody had just picked up some new mount, like a diamond unicorn or some such thing, and wanted to ride everywhere rather than teleport, so once they found out they were on a breadcrumb quest, they got out their horses and flying carpets and started moseying quietly along, fighting random encounters and piling up sacks of loot, even going so far as to continue to use their Teleportation to go back to town to sell stuff, but not to move ahead and get to where they were going, because they might miss out on loot. All told, it took them three weeks of game time plodding back and forth to get to the final Maguffin, a trip that I had sort of assumed would take them about twelve minutes.
In those three weeks, the populace of the world learned that their children were being born without souls and they had all been abandoned by their gods. Prayers were useless and priests had no idea what was going on… because once Our Heroes figured out what was going on, they DIDN’T TELL ANYBODY, and just got on their horsies and headed out into the wild… by the time they got back to Waterdeep, it was in ruins, as was every major city in the world, destroyed by riots.[/spoiler]
TL;DR version: The PCs find that children are being born without souls and the gods won’t say why. Nobody knows what’s going on and while the PC’s are riding across the countryside rather than teleporting everywhere, the world falls into chaos and destruction, paving the way for the 4th edition Faerun, a world of fallen civilizations and chaos.