- The (as of this posting) 2050 Things Mr. Welch is No Longer Allowed to do in an RPG
I recently got into an argument over whether it is possible to have a murder mystery in a fantasy RPG (or a transhumanist RPG, for that matter). The difficulty presented in a murder mystery is that the prime witness to the crime is, well, dead, so if being dead doesn't mean anything, where's the mystery?
You can still have murder mystery in a fantasy setting, though, as long as your culprit acts smart. What would be a perfect murder in an Agatha Christie novel is just stupid if the detective can brainscan the victim or cast Speak With Dead, so a clever murderer is going to take precautions against these.
For purposes of this post, we're going to be working off of D&D, since it's sort of a standard. Change out the spells listed and so forth for the equivalents in your own game. For instance, if you're playing Eclipse Phase, you can trade out everything in the spell limitations section for "pop their stack and run bedlams on it until they don't remember their own name, and establish an alibi". Also, these are going to be written as advice to a murderer in a fantasy setting; as a GM, hopefully you will be thinking about what your own culprit is doing.
- Spell Limitations. A lot of the spells that detectives use in fantasy just don't work under some conditions. Speak with dead and raise dead need a reasonably intact corpse, so at low levels, chopping up the body and hiding the pieces will do the trick. Resurrection calls for a part of the corpse, so at the level that becomes available, you need to do something harder, like burning the body or sinking it in the swamp. True resurrection doesn't even call for a corpse, so you need to either use trap the soul, find another way of keeping them from coming back, or trick the investigators into using the wrong spell.
Getting the investigators to use the wrong spell is deceptively easy. Just make them think that the body is fresher than it is (since these spells have a time limit) or in better shape than it is. Making a body look in better shape than it is is easy; after all, morticians do it all the time. Corpses are objects, so yanking out a vital organ and using a simple mending cantrip will do wonders (especially if you replace the organ with cloth or a slab of meat), or you can use the Craft (taxidermy) skill. If you're up against someone with resurrection, things get a bit trickier. For that, you need a statue of your victim and a stone to flesh spell.
Making the corpse look fresher than it is is easy too. Mending or taxidermy can reverse damage caused by rotting, and a flesh to stone/stone to flesh pair can keep it ready to pull out when you need a corpse. You don't even need magic either; just carve some ice out of the local pond in the winter and leave a fresh corpse in a room with it for a couple months. It won't look rotted, and unless the detective finds the ice room, they probably won't think it's been kept from rotting.
Of course, if you're making the murder look recent, you need to come up with an excuse for why it could be that fresh. This sort of thing's easy if you're a doppelganger or a master of disguise; just replace them and stage the murder mystery when you need to make your exit. It's a bit trickier, though, if that option's not open to you because you need to be elsewhere or can't disguise yourself worth ****. We'll assume for the moment that you haven't got a friend who can pull off the replacement. The easiest way to avoid raising suspicion is to have a confederate in the victim's household, either loyal to you, bought off/blackmailed, or dominated/modify memory-ed silly. The confederate can arrange excuses for why the victim isn't taking visitors: highly contagious and magic resistant disease, engaged in secretive and delicate magical experimentation for the rest of the week, out walking someplace, the excuses are limited only by your imagination. This works even better if you can cast modify memory on actual visitors every now and then; nothing like false memories to make people think the victim's still alive. And in either case, the alibi spell from Exemplars of Evil is useful for making people think you were someplace else when you were actually busy pulling this stunt.
Other spells have their own limitations. Detect evil can be foiled by undetectable alignment, or by not actually being evil (maybe you're just that nuts, or maybe the sonova***** actually had it coming, or maybe you're good enough that this won't push you to evil), or by everyone else nearby registering as evil. Glibness can fool zone of truth, as can carefully worded evasions. Clairvoyance can be beaten with false vision, or precise knowledge of when you can act. Even when your chambers (or those of your next target) are turned into a closed room with alarm, prying eyes, or blade barrier, you can still have your plots carried out using whispering wind, telepathic bond, hypnotism, or carefully arranged instructions; or you can break in or out of the sealed room with word of recall, passwall, greater teleport, a carefully timed still mislead or greater image, fog form, ethereal jaunt, or transport via plants, to say nothing of breaking Knox's third rule along with his second.
- Victim Limitations. Let's say that you have decided to ignore the above section, or that against all reason Our Heroes have figured out your trick. All is not lost! The trick here is to keep your victim from knowing whodunnit. There's some simple, nonmagical ways to do this, ranging from slashing your victim's throat in their sleep to using your death attack assassin class feature from behind to using poison or disease to rigging a complicated trap in their privy, but there's magical ways to do this too. You can kill them while disguised (either the mundane way or with transmutation or illusion spells), you can use the Deceptive Spell metamagic feat from Cityscape to keep anyone from realizing you cast whatever killed the victim, you can manifest death urge on them from where they can't see (or you can mask the display somehow), and if all else fails, there's always contingent modify memory set to hit them if someone brings them back to life. Or you could just, you know, hire an assassin so that the victim never has to see you.
- Victim Agenda. So the heroes have raised the victim, and you couldn't resist one last gloat. Either that, or there's now a ghost floating around. Or the victim was one step ahead the entire time, and named the killer in his will. Well, you may look ****ed, but this could turn out well. See, the victim could have their own plans. The victim might take advantage of this opportunity to advance a plot of their own, and implicate someone as their killer. And the suckers will probably buy it too. And nothing looks quite as bad as being named a murderer, or a kinslayer, or a regicide, by the victim himself. The only way you can count on this happening, though, is if you are the victim. That's right, I just said that the culprit and the victim might be the same person. A victim might make a suicide look like a murder in any number of ways, ranging from locking himself in a room with one other person and a crossbow, to having a guard slap him on the back and later jumping from a balcony with the intended "culprit" next to him, or any number of other tricks.