Writing a Case in City of Mist TTRPG  | City of Mist Tabletop RPG (TTRPG)

Writing a Case in City of Mist TTRPG

So you want to write a City of Mist case, one that will keep your players guessing and on the edge of their seats until the final showdown. However, figuring out how to write a mystery can sometimes seem more mysterious than the case itself! How are you supposed to come up with all the clues, locations, and characters you need?

Well, you’re in luck! We know that writing a City of Mist case is more than just figuring out who murdered who. That’s why the MC Toolkit comes equipped with an entire section on writing cases, and we’ll be going over many of those tips in this week’s video!

The Iceberg

Before you start writing, you should familiarize yourself with the iceberg diagram. This iceberg comes up quite a bit in City of Mist, as it’s a handy tool to chart out everything from simple cases to full on Avatar operations.

At the bottom of the iceberg is the truth of what actually happened and who’s involved. This is almost always a Rift using their powers in a harmful way, intentionally or unintentionally. If your crew of superpowered investigators were just going after some drug dealing Sleepers...well, that’d be like playing Dungeons and Dragons and fighting a regular komodo dragon. 

At the tip of the iceberg are the hooks that get your players involved in the first place. Once they start investigating, they begin to uncover the rest of the cases’s backstory as they dig deeper and deeper. How deep the iceberg goes determines how involved the crew becomes in the case, with each new Depth revealing important information.

Every location and major character involved in the case should appear on the iceberg diagram. This not only makes it easier to keep track of all the details, but it also gives you a roadmap for how the players can investigate the case. That said, you shouldn’t try to ‘railroad’ your crew onto the specific story paths in your diagram. Inevitably, they’ll miss some clues or come up with something that may skip over what you had planned. If they solve the mystery quicker than you expected, good for them!

The Backstory

Even if your crew go off the rails, having a complete backstory prepared for the case will help keep things in line. Whatever your case is about, your backstory should answer this question: What happened before the crew got involved in the case?

This is where most of the creative work comes in. You need to figure out what the crime was, who was the Rift responsible, and what kind of case you want this to be. Is this a murder mystery whodunit with the Rift of Colonel Mustard in the ballroom? It’s up to you! And if you’re having trouble coming up with ideas, you can check out the free City of Mist Case Generator for a variety of tables to help you out.

Once you’ve got an idea of the crime, you can begin fleshing things out. Ask yourself all the who, what, when, where, and why questions you can think of. But above all, make sure you have a timeline for the important events that have gone down. Your crew will inevitably ask a question you’re not prepared for, and the timeline is just one more tool the MC can use to keep the facts straight.

The Clues

Hopefully your crew will be taking notes as well, because any good mystery is solved by uncovering its clues. Now that you have an idea of what happened before the crew got involved, you can now shift your thinking toward how the crew gets involved.

When thinking about the start of the case, consider multiple hooks to get the crew’s attention. Your crew can be informed of the crime directly or just stumble on it. Keep in mind that your crew members may have different motivations, so consider additional hooks that affect one or two members personally. If Detective Enkidu hears about a crime in Precinct 23 and Baku hears about one of the students from his Tiger Claw Dojo going missing, they’re both going to want to solve the case by any means necessary.

Now it’s just a matter of connecting everything. Break down your backstory into the different locations and major characters, with each having at least one clue that will lead the crew further down the Iceberg. Your crew will be investigating the iceberg from the top-down, so each Depth is going to have more and more valuable information leading to the truth in the bottom.  When you write a clue, start with where you want it to lead the character next or what you want it to reveal; then, write the fluff around it of what it actually is: an object, a witness, a residual aura, etc.

Remember that clues can be anything, from physical evidence to paper trails to witness testimony. Be sure to keep the powers of the crew in mind as well. If you’re writing a murder mystery, you’ll have to account for the PC who can talk to dead people unless you want them to just ask the deceased who killed them. You’ll also want to prepare multiple paths and more clues than you’ll think you need, as it’s always possible your crew will miss something.

The Dangers

So with your backstory figured out and everything connected on an iceberg diagram, there’s just one last step. To make a real City of Mist case, you need action, and that means Dangers.

We’ve talked about using Dangers before in our videos and how they can turn a simple investigation into an action-packed thriller. A Danger can be a Sleeper or Rift, and can be someone actively hostile to the crew or someone who just gets in their way. Dangers can also be locations, like a burning building that the crew must now escape.

Ask yourself who or what could endanger the investigation. With everything else about the case lined up, it shouldn’t be that hard to find where you can put an obstacle. If one of your locations is a casino, put a bouncer at the door to deny the crew entry. If the investigation goes toward the docks, maybe the dockworker’s union is a corrupt mob.

Don’t be afraid to get a bit weird with your Dangers or even throw in an unrelated Danger on the side. It’s one thing to scope out a crime scene, but it’s another when a group of cops who are musketeer Rifts start interfering with your crew’s investigation. Now the scene is more interesting and calls on the crew’s social skills as well as their investigative skills. As the MC, remember you have all of fiction to draw from, so get diverse with your mythoi and really fill out your City.

Finally, remember to also add triggered scenes where the Dangers come looking for the crew. The villains and crooks of the Case aren’t just sitting around waiting for the crew to solve the case: they can go on the offense or try to destroy evidence WHILE the investigation is going on. Every good case should have trouble coming to the crew once or twice.


There’s a lot more advice I could give on writing a case, but hopefully this video helps you through the hard parts. If you’d like more resources on creating cases, be sure to check out the MC Toolkit along with the expansion Shadows & Showdowns for a variety of Dangers and hidden City locations.

What other questions do you have about writing a case? Let us know in the comments, on social media, or on the City of Mist Discord. Until then, have fun!

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