The PC hear about this incident by a rumor picked up while wandering through a city, or over a tankard in an inn.
Among the destitute of the city’s slums come rumors of a monster composed of live, writhing rats. There are claims that it has attacked those walking the alleys and closes at night, robbing them of valuables to take back to it’s fetid hovel. This was little more than a fanciful rumor until children started disappearing.
In truth, one of the town’s rat-catchers has been dressing up in a costume made of rat corpses as a scheme to rob drunks and whorehouse regulars. He crossed a strange line one night when he scared off an assailant preparing to murder a small boy who had stayed out too late at night. The boy told his friends, and the reluctant hero became an icon to the poor and wayward children of the slums. They are now sneaking off into the sewers to spend time with this newfound celebrity – and while the bewildered rat-catcher poses the young no harm, the things that dwell in the sewers just might.
The most likely course of action for the PCs will be to hunt down this “monster” where the rumors say it lairs. A hunt through the sewers will likely result in run-ins with rats and were-rats. When the PCs eventually catch up with “The Beast” they might chase or even attack it. But when the “Beast” here’s a child’s shout from down another winding drainage tunnel, the rat catcher reveals himself, and beseeches the PC’s help in rescuing the youngster (either from a danger of the sewers such as drowning or falling debris; or from a wandering otyugh lurking in the filth beneath the city).
What the PCs choose to do with the rat-catcher afterward is the real tension of this Incident. Technically speaking, the rat-catcher is a robber, making much of his coin from his bizarre muggings. At the same time, he isn’t guilty of murder or kidnapping, and happily encourages his adoring fans to return to their worried parents. He will protest any demands the PCs make to cease his ruse, but is in no position to really oppose them. Clever and compassionate PCs will find a way to convince the rat-catcher to end his crime spree while finding some more worthwhile income for himself (perhaps collecting a reward for rescuing the children, or offering to serve part-time at a temple or orphanage).
Possible EXP and Rewards
Because of the necessary legwork and NPC interaction, grant experience equal to two monsters of the PC’s level. There might also be a reward in gold for the safe return of one or more children. Perhaps the rat-catcher, thankful for staying alive and out of the stocks, passes along some equipment or a magical item he came upon while scouring the sewers for his quarry.