There is a small and strange nature-worship cult that has dedicated itself to freeing vegetables. They appear usually in working pairs or trios, arriving to villages and towns separately and wearing the local garb. For some reason, they have taken to disguising themselves specifically as a scholar, a cooper, and a fisher. At night, they will sneak into backyards and side gardens, digging up household fruits and vegetables. They pile the pilfered plants into a cart and vanish in the night. While the townsfolk wake up to empty gardens, the cultists replant the fruits in the wild to let them be "free".
A vicious murder happens in a town that the party happens to pop in at. Under heavy suspicion as they are strangers, the party is forced to discover the perpetrator or have their reputations blackened, especially as more and more murders occur in the town, and mysteriously stop and restart when the party leaves to go kill off that evil necromancer who kidnapped the princess.
The only problem is that a demon, possessing one of the party, is the perpetrator. And the demon makes no signs that its living in the PC's head.
In fact, for all the party knows (except for the possessed person's), their companion is an evil murderer.
Do they try and execute their friend as he's a vicious murderer, and no evidence points to demonic posession? Or do they flee town with him, trusting him, and have their reputations destroyed?