When I last posted, I described how to structure an extended investigation. In short, you need to start with your core adventure design. Decide what things your heroes must learn in the investigation; your adventure simply can't proceed unless they learn these two or three (or however many) things. Then decide what things they might learn in the investigation that would be helpful but not mandatory; maybe there's two to four of these. You made your list of "musts" and a list of "mights."

What now?

Mind Your Budget
First, you want to be keeping in mind your overall adventure budget for encounters and treasure and the like. Maybe you're planning this to be just one session to advance players about a third of a level or so; maybe you want to spread this out over a whole level. That's up to you (or your developer, if you're writing for someone else!). You investigations have to meet your budgets, in these ways:

Non-Combat XP: Your heroes should get XP for each of these things they uncover. Finding clues might be the single most common source of "story XP" that games grant! In PF2, I might award 80 XP for each "must" clue discovered and 30 XP for each "might" clue; in other games, maybe XP equal to a standard combat encounter for each "must" clue and a third of that amount for each "might" clue. This should give out plenty of XP (as the heroes should, indeed, learn a lot from investigation), but keep in mind that not every group will hit every "might," so they're unlikely to get it all--add more than your budget needs.

Combat XP: You should also plan to sprinkle in some fights, as necessary for your XP budget, keeping in mind that fights you put in the "might" locations are ones the heroes could miss, and thus not get any XP for. You're better off ensuring that the basic number of fights you need are in your "must" encounters. You can even double up (or triple up) fights in one of your "must" encounters, such as by putting in a short encounter area with a brutish or animalistic guard, a trap, and then an intelligent foe who knows (or defends) the information the heroes are seeking. Short strings of encounters like this are great additions to give the combat-oriented players something to do during investigations.

Treasure: As with the combat XP, keep in mind that any treasure you put into the investigation could be skipped if it's in a "might" encounter. You should probably put your budgeted treasure mostly into your "must" encounters, or even provide them as a reward for finishing the investigation itself.

This helps you frame out what each of your "must" encounters and "might" encounters should contain. You may have noticed that I stopped calling them merely your "musts" and your "mights," and I started calling them "encounters." That's how they should be taking shape in your mind: as a series of separate encounters that, together, make up the investigation.

Build the Connections
Second, you need to decide how every encounter is going to fit together. That is, to establish how the GM leads players from one to the other.

At the top of your list, write "START" to indicate where the investigation begins; normally, an NPC gives this start ("the king is suddenly doing a lot of uncharacteristically evil things these days, can you heroes find out why while you're guests in the palace?") but sometimes a situation does ("these people were all murdered during the night in the common room of this inn--what could have happened here?").

From there, draw arrows to each encounter this start position can plausibly lead to, once the players are as fully informed as they're going to be. You should have at least 3 arrows; investigation encounters are best when they give players choice right from the beginning.

Then, each of those encounters should point to at least one, but preferably 2 or 3, other encounters the heroes can pursue. It doesn't matter if two choices point to the same encounter (checking out the stable shows a torn uniform of the messenger's guild, and looking through a murder victim's belongings reveals a new, unopened missive from the messenger's guild). This duplication is good for the investigation experience: if players miss one clue, they can always find another, and if they already have that clue, they get some reinforcement that they're on the right track!

Keep building out this web, connecting your encounters. You aren't done until:

* Every "must" encounter has at least 3 arrows pointing to it. This is known in adventure design parlance as the "three clue rule," and I've talked about it before.)
* No more than half of your encounters are dead-ends that require backtracking (that is, one or more arrows point to it, but no arrows lead out of it).

At the end of this exercise, you'll see that your encounters--whether "must" or "might" encounters--have a logical order, like a flowchart (albeit one that loops back on itself several ways). The START NPC or situation gives the task, then leads to each encounter that would logically follow. Then you'll see the encounters that would logically follow from those, and so on. The farthest end of the "web" of encounters, which is the last encounter the heroes are likely to get to (probably a "must" encounter), is the one you'll present last.

Reorder your list to present each of your encounters in this new order, but keep the web between them intact! Presenting them in this order will help the GM who's reading through the investigation think naturally about the order the encounters should flow. That helps the GM run the game better. So you should set them in your mind as having this order before you even start writing them up.

Here's a secret: you actually don't need to flag the encounters as "musts" or "mights" any longer. You've already designed your investigation so that (i) XP and treasure necessary to meet the budget naturally pools in your "must" encounters, and (ii) the "must" encounters have lots of ways to reach them, so the heroes stumble across them in several different ways as the investigation plays out. It's not wrong to put in a sidebar or intro paragraph about "here are the critical things the heroes must learn during this investigation..." but you won't have to.

Okay, you've got your list all organized into encounters that connect to each other. Writing up the connections is the longest part, and some guidance on doing that comes in my next blog!