Investigations
Introduction
Investigations are prolonged skill challenges that take place over the course of an adventure. In most supplements, this is factored as a story award of experience. However, I prefer a bit more structure so I have the following rules in place. At the heart of any investigation is to uncover a single mystery, being the details of a series of events with the typical questions (who, what, when, where, why & how) answered. The progress of conducting an investigation is based around clues and theories.
Clues
A clue is any piece of information that is critical to solving the investigation. Each clue has two required checks: discovering a clue and identifying a clue. Most of the time, these checks can be retried and take the same amount of effort as a normal check of the same skill. Clues come in a range of difficulty: Easy, Average, Difficult, Hard and Impossible.
Discovering a Clue
Discovering a clue is usually based on searching. This typically a Perception check, but can also be Appraise, Diplomacy, Sense Motive or Survival. Regardless of the check required, the check can only be attempted when the investigator is in the vicinity of a clue. The Investigate feat gives a +2 circumstance bonus to any check involving discoverying a clue. In many cases, it is not just enough to be searching for clues, but you must also be in the correct location. If time is a factor, assume a single 5' cube of space can be quickly searched in a move action (+10 to the DC) or thoroughly checked in 1 minute. It is possible to retry looking for clues, but if time is a factor, each failed attempt increases the DC by +2.
Identifying a Clue
While discovering a clue is important, ultimately, it is unhelpful until it's relevance has been correctly identified. Identifying a clue requires an appropriate Knowledge check, as determined by the nature of the clue. Like normal Knowledge checks, they cannot be tried untrained if the DC is above 10 (or 15 for your region of origin). However, the Investigate feat allows the Knowledge check to be tried untrained for this purpose. Once a clue has been correctly identified, it can be used in a theory.
Knowledge checks cannot normally be retried, but use of certain class features or the use of a library can be used to allow that option. See the Research Feat and the new uses for Knowledge Skills for details.
Theories (Beating an Investigation)
During the course of an investigation, party members will probably come up with a large number of theories, just like real investigators do. Not all of them will fit the clues discovered. Others will fit, but see unlikely. In order to solve an investigation, the party must successfully discover and identify 75% of the clues involved in the investigation and then propose the theory that is close enough to the correct one that the only differences are semantics.
Creating a Investigation Challenge
In order to create a investigation challenge, follow these steps.
Determine the Base EL
Start with determining the base Encounter Level (EL), just like you would for determining the EL of a combat encounter for the party, given their Average Party Level (APL). This will determine the base DC for both discovering and identifying the necessary clues.
Determine the Number of Clues
Next, determine the number of clues for the investigation. When choosing this, it is important to expect that the party will not discover more than a few clues per session (recommended max: 3) and thus it will also give you an idea for how long the investigation will take. It also adjusts the final EL.
Define the Clues
Defining the clues will be the hardest part of the investigation. This process will not tell you how to design your mystery, conspiracy, etc (although I do recommend with writing down what really happened and then work backwards, looking for spots were the villain could make a mistake). Defining the clues, as per this guide, is about determining the DCs for discovering and identifying the clues, base on the number of clues you have decided one. Use the following table to see how many clues you have to work with.
Once you know how many checks you have, the DC for each check should be in the following range. Each clue has two checks, but the DCs for discovery and identification do not have to be in the same category.
Easy: Base EL +7-10
Average: Base EL +11-14
Difficult: Base EL +15-18
Hard: Base EL +19-24
Impossible: Base EL +25 or higher
Complications
Very few investigations are done completely independent of another factors. While combat is always a valid complication to an investigation, it is not the only one. While combat should be handled separately (and factored separately for XP), here are some other ways to complicate an investigation outside of combat.
Reward: If the party takes on investigations for other NPCs, they should be paid for their effort, just like the wealth per encounter of the same level. If the idea of putting down a retainer comes up, the maximum to be expected is 25%.
Time Table: If the investigation needs to be completed before a specific deadline, that can significantly raise the difficulty for success. For example, finding out where a little girl was taken to and getting her back is not nearly as successful if she has already died while in captivity. If the investigation is not completed by the end of this period of time, but can still be continued in a less effective manner, recalculate the EL adjustment. If the investigation is not completed in time and it cannot be continued in any effective manner, the party fails the investigation encounter. Kind GMs may award between 25-50% of the normal XP.
Use the following table for an estimated guideline. By default, always assume a reasonable time table.
Personal Loss: If an investigation has the threat of loss upon failure, that pressure will drive the party faster. This loss does not have to be personal in the strictest of sense. It can be threats made to an ally or contact, the reputation of a loved one or family member, the harm (or death) of an innocent. What matters is how much that loss would affect the party or individual party members. In this sense, good characters have more to loose than evil characters (not to say that evil characters do not have anything to loose). Use the following table for an estimated guideline. By default, always assume a minor threat of personal loss. See Prestige Awards for details on CPA and TPA.
Finalizing the Investigation
At this point, determine the final EL for the investigation and use the number of clues, checks and complications as a guideline for writing your investigation.
Running an Investigation
It is recommended that before you start an investigation encounter that you have the winning theory detailed completely, as well as clues necessary to get to that deduction. Investigation encounters are complicated enough that they typically require 3-5 times the normal amount of GM prep time and should not run ad-hoc. Unless your party has a dedicated note taker, I recommend getting a stack of 3x5 index cards with each one detailing a clue (including location, importance, etc). On the edge of each card, detail any other clues or important questions that clue should point to. The idea of this is that players that come back to an investigation session after a week (or two or three...) find it easier to physically look at a puzzle, rather than read through notes.