A heist job.
The PCs are forced to kill, whether or not they want to.
At a pivotal moment, an NPC from one PC's past shows up - or maybe just somebody who convincingly pretends to be one. They reveal information that makes it sound like the PC has been conspiring against the rest to split the hall with the NPC.
Thing is, the NPC is lying. But is very convincing.
In effect, you orchestrate a situation in which evil characters begin to infight. And because they're evil, it creates lots of opportunity for highjinks.