1. The On-The-Fly Approach
I've mentioned before how I like to run a mystery:
- DM develops a general idea of "what is going on"
- Clues/leads randomly generated or made-up on the fly for the PC's as their investigation advances
- These lead to further people/places with more clues/leads
2. The Masks Approach
But there's another approach: the Masks of Nyarlathotep Approach. And it's all about Master Craftsmanship. Here, the clues/leads are painstakingly prepared in advance, with actual pictures/text to cut-out and give to the players. To give you an idea of the amazing design-work that went into this, here's a graph of clues and the people/places/things they lead to constructed by one dedicated fan. Keep in mind that the adventure has 5 such locations:
My On-The-Fly approach is clearly easier to prepare/run. But Masks' approach means that you can actually give players a physical clue to hang-on to, that they can analyse in detail and will actually remember between sessions. Thus the game becomes less about killing stuff and taking their treasure, and more about putting together all the clues and figuring out the mystery.
3. The Player Skill Problem
As I mentioned recently, one of the difficulties in running a mystery is that of Player Skill.
Player Skill- solving mysteries can be difficult, and additionally, what seems obvious to the DM may not be to the players. So what does the DM do when the party is stuck, besides throw a tasteless Deus Ex Machina at them?
Both approaches above deal with this problem in different ways:
In the On-The-Fly Approach, I randomly generate clues for each location, so that even if the players miss a critical clue at some location, they may still find another one elsewhere.
In the Masks Approach, there are so many clues that even if the players don't find them all, they still have a good chance of finding some clue to advance them in their investigation.