The hyperborean realm of the Eternal Flame
Clarence was singing in harmony as his kind is wont to do. Their singing reinforced the "song of existance". It was a somewhat important job, even though only a handful were needed rather than the hundreds that did so. He and others near him noticed the pin prick discordence in the weave of melody that was the material realm. Those dark alien notes rose up. The Angel Mind touch the Divine and followed the new sub melody. Humans would call it a plan. Angels dove to the material realm and, of course, if any world was going to be causing problems, it had to be Earth. Oh well, at least Clarence would know his way around.
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?