The Liberators of the Coin is primarily an organization Halflings devoted to (insert trickster/thieving/Halfling god). They pattern themselves after a myth of the god stealing gold coins from his brother on the evening of his wedding. The stolen gold was a part of the wedding ceremony and its absence meant that the ceremony could not proceed. The theft resulted in the trickster being able to marry his brother’s intended.
Far to the north, past the cold, vast plains and tangles ancient forests, past even the brooding Deadfire Mountains, lies a real of ice and bitter cold. Barren and stark, few have ventured in to this icy realm. Hunting here is scarce and the wind seems to howl with the voices of demons. Yet there are rumors of a citadel in the heart of the ice field, rising above the wind-swept whiteness and glittering in the pale sunlight. Some say that the citadel was built of block of ice by giants. Others claim that some wild magic caused the structure to grow from the very ice. Yet others state in low voices that it is not ice that shines so, but a fortress of diamonds, built in ages past to guard the most powerful of magics in the world.
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?