Treating a mystery like a dungeon - Random Encounters

“When in doubt, have a man come through the door with a gun in his hand.”

-Raymond Chandler 

Here's something I've been thinking about lately: Are there any ideas from OSR Dungeon Design that we can take and use to improve our mystery games? 

Dungeon design has recieved a huge amount of discussion and refinement over the years, and there may be some fruit we can pluck for other genres. Here's one thought from this vein:

Random Encounters

Roll for encounters every time the PC's perform a major action, and whenever the PC's do something that could draw the attention of the malevolent forces behind the mystery.

Major actions are things like moving to a new location, spending time researching in a library, or engaging in a fight. You can think of each major action as one "Scene". 

To roll a random encounter, roll d6. On a 1, an Encounter occurs. On a 2, an Omen occurs (signs or hints of an encounter).

Each adventure would have a random encounter table, but here is a simple example that could be used for any Film Noir style mystery where the PC's are tangling with an evil organisation. 

Encounters

1. A thug bursts through the door, firing a gun. They plan to kill whoever the PC's are talking to, in order to silence them - then escape.
2. The bad guys sneak in and bug the PC's phones or lines of communication.
3. The bad guys ransack the PC's home or place of business. They will steal any valuable items or information the PC's have. 
4. An NPC with vital information is kidnapped. PC's will be sent a letter with demands ("Leave town or we kill them", that kind of thing). 
5. One of the PC's friends or contacts is bribed to turn traitor. They will feed the PC's incorrect information to send them into an ambush.
6. The PC's car or method of transportation is rigged with a bomb. It will explode the next time it's used.

The encounters should be dramatic moments where the NPC's advance their goals or try to stop the PC's investigation. 

Omens

1. There are signs that a low-ranking person from the bad guys was just here (footprints, cigarette butts, car tyre marks, graffitti, things like that). 
2. There are signs that a high-ranking person from the bad guys was just here (footprints, cigar ash, witnesses saw a fancy car, things like that). 
3. A group of thugs trail the PC's in a black car. They will attempt to escape if the PC's catch on.
4. A high-ranking member of the bad guys begins to follow the PC's, pretending to read a newspaper. They will attempt to escape if the PC's catch on.
5. The NPC's in this area are frightened. They've just been intimidated by the bad guys. 
6. One of the PC's friends or contacts starts to feel like they're being watched. The bad guys are staking out their house.

The omens should be clues that foreshadow danger and give the PC's a hint about your mystery. 

In a real adventure you would customise the table to your needs, with 6 encounters and omens that fit your mystery. In a lovecraftian adventure, you could also roll for an encounter whenever a PC interacts with the mythos (Eg, saying Hastur's name aloud). 

How to write one yourself

One easy way to start is to make a list of the important pieces of information that hold up the mystery. For example:

1. The Duchess is having an affair with Lady Aubergine
2. Lord Smothersberry was smuggling in cocaine through the docks
3. Lord Smothersberry was killed by Lady Aubergine in a duel
4. ...

Etc, etc. Try to make a list of 6 pieces of important information. Then, create 1 encounter for each piece of information. Each encounter is related to that piece of information in some way.

1. The Duchess attempts to destroy any evidence the PC's have gathered (raiding their home base, burning papers, etc)
2. Lord Smothersberry's smugglers confront the PC's, attempting to rob or silence them
3. Lady Aubergine tracks down the PC's and challenges one of them to a duel.

Finally, use this list to create the list of Omens. The omens can just be signs or clues that are relevant to each encounter.

1. Signs that the Duchess has been here recently.
2. Signs that the Smugglers have been here recently.
3. Signs that Lady Aubergine has been here recently.

Etc. It should be pretty quick and simple to write this up for a published adventure, as long as you know the key pieces of information you need. 

The benefit of this approach is that it makes sure your encounters tie in to the core fabric of your mystery - they aren't red herrings or distractions, they are moving the game forward in a meaningful way. You don't have to follow this though - you could also make a list of the core factions or NPC's in your mystery, and make encounters that relate to each one.

The Benefits

I think this does quite a few things elegantly.

1. It makes it feel like the NPC's are actively working towards their goals. 

It's easy for a mystery with many moving parts to feel a bit static. The GM has a lot going through their mind. It's tough to think about what all the different NPC's would be thinking and doing while the PC's are investigating.

The random encounter table does this for you. You just fill it with entries that represent the NPC's attempting to complete their goals (For example: Lady Blackbeard finally hunts down the amulet of Zorathstra.) It makes the situation feel dynamic and vibrant without needing to spend a ton of work.

2. It creates a time pressure and forces the PC's to make interesting decisions.

Again, time pressure is something critically important that can be hard to pull off. If there is no time pressure, there's no tension, and the PC's can spend all the time in the world doing whatever they want.

Some mystery adventures have specific timelines - the ritual happens in 3 days, this happens at 11:30, etc. This is handy, but it can easily go off the rails if the PC's go off-script. 

An encounter roll gives the PC's that feeling of time pressure constantly and easily. Just like a normal dungeon, you should be transparent and open with your PC's about this. "Yes, you can read through that occult tome, but it'll take some time so I'll roll an encounter check. Do you still want to do that?" 

And as a bonus it adds a nice push-your-luck element, because you also roll if the PC's do anything that is likely to draw attention from the malevolent forces behind the mystery. "Yes, you can infiltrate the mob's speakeasy, but that's likely to draw attention so I'll roll an encounter check. Do you still want to do that?"

3. It keeps the mystery moving.

If you run into a situation where your players have hit a dead end and don't know what to do next - that's when you can pull out a random encounter to push things along. 

All of these encounters should, of course, come with clues that help push the PC's towards the main mystery. The man who comes in firing a gun has been sent by the mob boss. The PC's can interrogate him for information or follow him back to his lair or find evidence on his body. Either way, things are moving.