Following up on my previous thread on a fantasy/psychological thriller/murder mystery idea I had, I was wondering about how to handle "illegal actions." To clarify, a group are sent to an isolated "paradise"-esque environment on a private vacation sanctioned by their mutual employer. Not being known for his kindness towards them at all, the group are initially skeptical, but in the end accept the change. Of course, in time, the killings begin to start, and even though they're first suspicious that the aforementioned employer is the culprit, various clues point towards a completely separate individual... I suppose its a relatively basic set-up to a murder mystery -- I'd like to accredit that to the fact its still very much a rough draft. However, my issue is the very last part; I do want the clues pointing towards that person to be a red herring, however at the same time, I don't want it to be a twist as obvious as everything actually being masterminded by the employer. I thought an interesting idea could be deterring the audience away from suspecting who was initially thought to be the murder with them in turn being killed, but I felt it'd be too obvious as well. so my idea in the end was: There's only a single human who is a deliberate murderer. However, even if he is the killer, and dies very early on, clearly deliberate deaths still occur. The way I thought to explain this is "illegal actions." These are actions which trigger the person's death and are unique to each individual. My issue is a number of different things: How would I go about deciding each person's "illegal action"? How would I explain the presence of these "illegal actions"? How could there be deaths that're simultaneously caused by an external force of some kind but also paradoxically be the actions of a person in this isolated environment without a conclusion as tacky as "they were being controlled"? If characters don't know about the presence of these illegal actions, how would I go about foreshadowing their existence? How and why would these exactly be actions that trigger their death? I do have a faint idea about how these concepts will attribute to the overarching narrative I have in mind. I, however, merely have an issue with filling out the more finer details and the more absolute conceptualization.