A tribal society which lives on the harsh Northern Plains consider it dishonourable to slay an enemy without looking it full in the face. Any missile weapon is treated with derision and contempt, while rangers and other archers are denied entrance to the tribal villages.
The population of a forested kingdom never reveal their names to any but their immediate family, and consider it a grave mistake when others do so.
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?