There’s no better way to celebrate Halloween than to run a murder mystery one-shot for your D&D group! In fact, my group is coincidentally playing through one right now. It was the first murder mystery I’ve ever created and I have learned a ton throughout the entire process of building it and running it.
As you can imagine, murder mysteries, or any other mystery for that matter, are very different from the average dungeon delve or adventure.
There are so many moving pieces that you have to write and keep track of. Especially in a game like D&D 5e where spells and magical items can throw a wrench into the mystery at any moment.
But, well-written and executed murder mysteries are one of the most fun things you can pull of as a DM. The players will feel clever for figuring it out, and you will feel very accomplished for being able to pull it off. Plus, hunting down a mysterious killer is about as on-brand as you can get for a Halloween D&D session.
What is a Murder Mystery?
For those of you that don’t know, a murder mystery is a specific type of mystery. As the name implies it has both a murderer and a murder at the forefront of it.
Typically what happens is that there is some sort of event, party, or function that a group of attendees go to. Generally, the attendees don’t know everyone in the room or may not know anyone at all. At some point during the event, a murder is committed and extenuating circumstances prevent the authorities to be called and the guests to leave the premises.
Logically, it’s up to the party-goers to figure out who the murderer is and bring them to justice! But, there is always the lingering fear of the murderer striking again. The closer the group gets to figuring out the murderer, the quicker they strike.
One of the most famous examples of a murder mystery is the game Clue (or Cluedo apparently for those outside the USA). There’s a mysterious murderer in the midst of the group, but there are clues that the group can find to help them deduce who is guilty.
Step 1: Decide Who the Murderer Is
Create a Murderer
The first thing you want to do when writing a murder mystery is to decide who the murderer is and why they are killing everyone at the event. Murder mysteries become complicated quickly. Your NPCs will constantly be interacting with each other and the players, and there are a ton of different clues to keep track of.
You can write yourself into a loop very quickly with so many different variables to keep track of. So instead of writing everything from the ground-up start at the finish line of the adventure and work your way backward. Who is your murderer and what happens when they are caught?
Once you have figured that out, flesh out the murderer. Make them unique, but have them blend in amongst the other suspects that the party will be interacting with. You want them to be memorable, but not someone who jumps out to the party as “the murderer” after they have a single conversation with them.
I’ve written a post on how to create a great D&D villain previously if you want some more direction on creating a memorable and deadly villain.
Create Their Motive
Every good villain needs a motive, especially a murderer that does their work in the middle of a party while they’re actively searched for. They need to have a solid reason to want to murder everyone at the function.
Jealousy or greed are probably two of the best motives. Someone at the event has something the killer values such as information or a prized possession, and the murderer needs to kill them to gain whatever it is they’re after.
The setting could also be in a place filled with expensive items and the killer panicked while stealing one. The subsequent murders are a desperate attempt to get rid of the witnesses.
Another great motive is revenge, particularly revenge against the host. The murderer hates the host and wants to systematically kill all of their friends and loved ones. What better place than at a party with everyone on the guest list?
Regardless of what you do, make sure that you give your murderer a motive that makes some sense. Suspension of disbelief is prevalent in murder mysteries, but at least make a solid attempt to give your murderer a motive to make them a more interesting villain, or at least to open up some future plot hooks.
Step 2: Create the Setting
Why is the Party There?
There has to be some reason for the party to end up at the place of the murder. Ideally, they will be at the location before the murder takes place to solidify their spot in the plot. You want the NPCs to potentially be suspicious of not only each other but the party as well.
This can create friction, but it also gives the party a reason to look for clues and speak to everyone. If all of the NPCs are biased or unreliable they’ll have to do a lot more problem solving and hunt for more concrete evidence.
Give them a reason to show up at the location. Meeting a person, rubbing elbows with movers and shakers, or scoping out the location for a future heist of their own are all reasons that they would both show up to the scene and have a vested interest in finding the murderer.
You could even use a MacGuffin to lure the party there. Perhaps it was an auction for art or rare items and the killer is looking to steal a valuable item!
Why Can’t Everyone Leave?
In my opinion, there should be something unique about the setting that creates the perfect circumstances for a murder mystery. It has to be at least somewhat believable that the party and the other guests a) cannot leave the premises and b) cannot call the authorities to solve the case.
It could be that the party or function takes place in a place outside of civilization. They can call on the authorities or the guards, but it will take them a few hours to arrive. By then the murderer could have killed them all one-by-one!
On the other hand, maybe everyone at the party is suspicious of something and has a reason to not call upon the guards. Or, a natural disaster or a storm could strike forcing everyone to stay within the confines of the mansion they are in.
People being able to leave or call the authorities changes the premise of this from a murder mystery to a mystery that involves a murder. It’s a classic part of murder mystery games to have everything quarantined in a single location.
Who Are the NPCs?
Creating all the NPCs was one of the most fun parts of writing my murder mystery. You want your NPCs to be diverse and unique both from a “good NPC design” standpoint and for making the murder mystery possible.
If there’s a single NPC that sticks out like a sore thumb to the party it’s possible your adventure is over before it even began.
What you want to do is to create a decent amount of NPCs that all have either a potential motive/capability for being the killer, or have a few red flags that will cause the party to suspect them. For my murder mystery, I settled on 8 NPCs, but you can do as many as you’d like.
The more NPCs you have the more convoluted the mystery can get. The NPCs shouldn’t just interact with the party. They should be interacting with each other as well as the environment around them.
Step 3: Add Clues
You know how it goes. The lights go out in the room. Someone screams. The lights come back on. The body of a party-goer is on the ground while everyone else is sitting or standing in the same spot you saw them previously.
At first, it could be presented as a freak accident, but the killer was rushed. They left their murder weapon or device behind for the rest of the group to find.
The murder weapon is most likely going to be the first and largest clue that the party receives. It could be something as obvious as a knife sticking out of the back of the deceased, or it could be residue left over from the poison in their drink.
Whatever the murderer’s method is it should be obvious enough that your players will know that this is a murderer and not some sort of freak accident.
The murder weapon can also give your party a lot of information. A person that kills with a knife is someone who’s not afraid to get close and personal with their target. Whereas someone that poisons a person’s drink is less confrontational and has a reason to hide in the shadows.
You should have a group of NPCs that are guests of the party just like the players. These NPCs can serve as useful tools for finding the murderer, or they could be people who actively hinder the party from solving the case.
The other suspects should be a diverse group of people. You shouldn’t have a pattern that the players can figure out when it comes to your NPC interactions. Each one should have their own personality and be unique enough that the party won’t get any of the NPCs confused. You don’t want to unintentionally throw your players for a loop.
That being said, don’t be afraid to add red herrings in the form of events or NPCs. These will be events or conversations that make a completely innocent person look extremely guilty of being the murderer.
The party will have to figure out if they are truly the killer or if they’re a dead-end, but either way, they will explore more and potentially find clues that they’d have otherwise missed.
Skill checks can be very helpful for finding secrets and learning additional information in D&D 5e. This shouldn’t be an exception when running a murder mystery in D&D 5e. PCs should always be rewarded for making a successful skill check.
However, when creating a murder mystery you should be sure that the mystery can be solved without the party passing a single check. It may be easier for them to solve the puzzle if they make a few clutch checks, but the entire thing needs to be possible to solve without rolling a single die.
You don’t want the entire adventure to hinge on someone making a single skill check. You want your players to figure it out using the clues they found and the information they gathered. Think of a murder mystery as more of a puzzle than a full-fledged D&D 5e adventure.
Notes, Trinkets, and Other Items
Throw in tons of clues! You’ll want more clues than you think will be necessary because I guarantee you your party misses at least half of them.
This follows the same principle as the “don’t rely on skill checks” rule. You don’t want your mystery to hinge on the party finding specific clues. If you do though, you’ll need to make these clues as obvious as the initial murder weapon to ensure that they don’t miss it.
Clues can be anything though. They can be tangible items like trinkets and things that the NPCs may carry around, or they could be pieces of evidence found near one of the murders.
Another kind of clue that’s common for murder mysteries is the bits of information learned through conversations with other party guests. People are nervous when they’re put in a stressful situation. It’s absolutely possible for someone to give out some crucial information when they didn’t intend to.
But information doesn’t have to be an obvious clue either. This type of conversation could help the players paint a picture of the other NPCs. They can learn about their mannerisms and personalities as well as any sort of suspicious behavior that they exhibit.
Step 4: Play it Out!
Use Your Notes!
Keep a sharp eye on your notes. There is a lot to keep track of for a murder mystery because there are so many pieces to the puzzle.
You have all the NPCs; their personalities, biases, and information about the other guests. All of the clues that are strewn about the setting and dispersed in different conversations. And most importantly, how all of this intertwines to give the party a path to find the killer!
As you go about, you’re more than likely have quite a few instances where you’ll have to improvise and ad-lib some encounters. This should always be expected when playing RPGs, but when running a mystery game it can be especially difficult to stay on task.
You want your improvisations to be both useful, and align with the information you have written down. The intent isn’t to railroad your players, but you want to make sure that your ad-libbing hasn’t thrown your players completely off-course and steered them away from solving the murder mystery.
Help/Nudge the Party if They Need It!
If the party is completely lost it may be a good idea to give them some more obvious hints or clues. Give them a bit of time first to make sure that they’re not just thinking things through slowly. You’ll be able to tell when they’re genuinely stumped or beginning to get frustrated.
While it’s clear to you who the killer it’s definitely not to them. The “obvious” hints that you’re throwing at them may not be so obvious to those without all the information that you have about the murder mystery.
Don’t be afraid to subtly push them in the right direction, especially if you can sense them being frustrated. From the player’s perspective, a mystery or a puzzle becomes unfun very quickly if you’re making no progress with it.
Giving the party a bit of help or some extra clues doesn’t mean that you’ve failed to make a good murder mystery. It could be a combination of things such as the party not finding all the clues, or mysteries aren’t really your players’ cup of tea.
On the other hand though, if it is a problem with your narrative structure or your clues weren’t helpful enough take note of that. Observe and learn how your players tackle the problem so you can go back to the drawing board and make an even better one next time!
Raise the Stakes!
As I’ve mentioned before, PC death can raise the stakes in your game and make things much more intense. While I would highly recommend against intentionally killing a PC during your murder mystery, the same principle can be used for the NPCs during this adventure.
Your murderer may opt to strike multiple times before the party gets a chance to stop them. Perhaps they’ll target an NPC or two that have gotten close to the party in an attempt to get them to stop investigating.
Killing off NPCs is one of the best ways to give the party a sense of urgency as they attempt to solve the mystery. The more time they take, the more NPCs perish. This can be especially effective if you give the party time to bond with a few of the NPCs. They don’t want to get their friends killed!
Figure out a way to get the party to figure out who the murderer is as quickly as possible. You want them to be on-edge and constantly trying to find new clues. As opposed to simply waiting for the problem to sort itself out.
Murder mysteries make for extremely fun D&D sessions, though they are a very different beast to tackle compared to your average D&D game. They require a bit of finesse in the writing and execution, but they’re not very difficult once you get into them.
Work from the conclusion to the beginning of the puzzle when you’re writing it. This helps you ensure that there is a straight path that connects the two. From there add side pieces such as additional NPCs, more clues, and other events and things that can aid the party in discovering the culprit.
You want to create a complicated web that can throw your players for a loop and make things interesting. However, you want to make sure that you are still able to untangle that web through a few different ways. Include plenty of clues and make sure that your players don’t have to make skill checks to solve the mystery.
Most importantly though, have fun with it! It’s a change of pace from a typical game of D&D, but it’s definitely a great way to spend a Halloween session!