TITLE: Lies, Lies, Lies
OVERVIEW: The PCs are convinced by an enemy that an ally is an enemy.
TRIGGER: Something bad happens to PCs.
DESCRIPTION: The players are told by a "witness" to the incident that {friendly NPC} had a large part in it.
DM NOTES: Their source of information is actually a spy/assassin/jerk (best if this is also an ally, well known to the players) who wants the PCs thrown to the wolves for kidnapping/murder/assault/etc. They try to blame the incident on one of the PCs closest acquaintances.
KEY: PCs could kill their friend and look for revenge.