Ran a bit of an unusual campaign: To summarize, the party consisted of a legendary group of resurrected heroes. The twist being, that the ritual to bring them back was imperfect, causing them to come back as ghosts capable of possessing people that touch items from their past lives. They're brought back in living bodies, so they don't realize this yet.
Anyway, the very first session started with them trying to escape their own crypt, as enemy soldiers tried to track them down and capture them for story-related purposes. They played things fairly smart, avoiding direct confrontations, spying on the enemy, and taking advantage of untripped traps in the dungeon.
Part of their eavesdropping lead to them discovering that a significant portion of the soldiers were actually evil mercenaries sent there to ensure that they and the other soldiers were killed. More story-related stuff.
So, they manage to reach the exit to find that a bunch of these mercenaries have taken up defensive positions there, with their
evil Gnomish captain on the watch. Upon detecting them, the Gnome called out to the PCs and claimed that he was with the local militia and that they were only there to talk. By now, I've given plenty of evidence that these are bad guys there to kill them.
So, naturally, one of my players decides that the 'Good' thing to do is approach them and try to resolve things diplomatically. Despite having interrogated one of the other mercenaries, seen the mercenaries kill the other soldiers, and having been almost killed several times by said mercenaries. The other PCs and even an NPC helper Homunculi they found don't think it's a good idea...
The Gnomish Mercenary gave a jovial wave, before ordering the archers to open fire on him. Three successful hits later, and the PC falls to the ground dead.
This was naturally the point where I revealed the ghost-possession twist to the group, but at the time the player was absolutely shocked that an evil mercenary would lie.
