You wake in a pub and see that it's full of were creatures, and they're all staring at you with a scared look on their faces. As you continue on into the pub you look at your arm. You notice that your arm is covered in thick brown hair. As you continue on into the pub you look in a mirror, and staring back at you is a 7 foot werebear. As you continue into the pub people start to shy away form you. Once you go the bar you ask the weretigress that's the bartender and begin to ask her why everyone is shying away from you, and she begins ro tell you why.
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?