You shall carry your sibling, be his support and guide.
He shall be your shelter, guardian, aegis firm.
United you stand, divided you fall.
Thie pearly material is also known by the sinister name of Demon’s Tooth.
“A man needs two things to become a saint. He must perform three miracles, and then he must die. Perform your miracles, sir, and come to me when you are ready to become a saint.”
—Azariah Saintmaker, Dread Lord of Hatred
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?