Investigation Mechanics

Investigation Mechanics for Horror RPGs

Running successful investigation scenarios requires understanding how players discover information and reach conclusions. This guide covers proven techniques from Call of Cthulhu, GUMSHOE, and other investigation-focused RPGs.

🔍 The Three Clue Rule

Core Principle: For any conclusion you want the PCs to make, include at least three clues.

Why Three Clues?

Mystery scenarios fail when players miss crucial information. A single clue becomes a chokepoint—if they don't find it or understand it, the adventure stalls. The reality of investigation gameplay:

Players will likely miss the first clue entirely
They'll overlook or dismiss the second clue as unimportant
They'll misinterpret the third before reaching the correct conclusion
Multiple clues provide redundancy and prevent single points of failure

Example Implementation

Conclusion: "The killer is Dr. Harrison's former lover, Elena"

Three Different Clues:

Love Letters: Stack of passionate letters in Dr. Harrison's desk, signed "E"
Diary Entry: Victim's diary describing a secret affair and recent bitter breakup
Photographs: Hidden photos showing Dr. Harrison with Elena at romantic locations

Key Benefits

For Players

Feel smart for piecing together evidence
Have backup options if they miss one clue
Experience "aha!" moments naturally
Investigation progresses at good pace

For Keepers/GMs

Prevent investigation from stalling
Track what players have discovered
Introduce new clues when needed
Maintain mystery without frustration

📊 Clue Hierarchies

Not all clues should be equally difficult to find. Organize clues into hierarchies based on discovery difficulty. This creates a sense of progression and rewards thorough investigation.

🟢 Obvious Clues

Investigators notice immediately without searching

Dead body in middle of floor
Blood trail leading to door
Strange symbols on walls
Loud supernatural sounds
Recently disturbed grave

🟡 Hidden Clues

Require active searching or investigation

Documents in locked drawer
Bloodstains cleaned but visible
Scratches on floorboards
Hidden compartment in desk
Faint footprints in dust

🟣 Expert Clues

Need specific knowledge or skills to recognize

Medical cause of death
Occult symbol meaning
Chemical composition analysis
Ancient language translation
Forensic evidence interpretation

💡 Design Tip: Include clues from each category for important conclusions. Even if players lack expert knowledge, obvious and hidden clues ensure progress.

🎈 Floating Clues

Floating clues aren't tied to specific locations or actions. The Keeper introduces them at their discretion when players need a push in the right direction.

How Floating Clues Work

Preparation: Designate 2-3 clues as "floating" for each major conclusion
Deployment: Introduce when players are stuck or heading down wrong path
Delivery: Present through active events (NPC contact, discovery, attack)
Integration: Make it feel natural, not like GM intervention

Floating Clue Examples

Witness Appears: Surviving victim suddenly contacts investigators
Enemy Attack: Cultists attack, revealing their connection to the mystery
News Report: Radio announces related incident in different location
Anonymous Tip: Mysterious note pushed under door at hotel
Chance Encounter: Run into suspect in unexpected location

⚠️ Use Sparingly: Floating clues are a safety net, not a crutch. Players should earn most discoveries through investigation.

⚙️ Investigation System Approaches

Different horror RPG systems handle clue discovery differently. Understanding these approaches helps you run investigations in any system.

Call of Cthulhu Approach

Roll to Find Clues

Players roll skills to find clues
Failed rolls = clue missed (potential stall)
Creates tension and stakes
Requires Three Clue Rule implementation

Best for: Groups comfortable with potential dead ends; atmospheric horror

GUMSHOE Approach

Automatic Clue Discovery

If you look in right place, you find clue
No failed skill rolls for core clues
Keeps investigation moving forward
Spend points for extra information

Best for: Story-focused groups; investigation-heavy campaigns

💡 Hybrid Approach: Use automatic discovery for vital clues, skill rolls for bonus information or shortcuts. This prevents stalls while maintaining mechanical engagement.

💡 Practical Investigation Tips

Preparation

List all conclusions before session
Create 3+ clues per conclusion
Mix clue difficulty levels
Prepare 2-3 floating clues
Map out clue locations

During Play

Track which clues were discovered
Accept creative investigation approaches
Reward clever thinking
Introduce floating clues if stuck
Never punish thorough investigation

Common Mistakes to Avoid

❌ Single clue per conclusion
❌ Hiding clues behind specific actions
❌ Deliberate red herrings
❌ Requiring specific skill uses
❌ Making players guess exact location

What to Do Instead

✅ Multiple paths to each truth
✅ Reward any reasonable approach
✅ Let players create own theories
✅ Accept equivalent skill usage
✅ Generous area searches succeed

✓ Golden Rule: The mystery should be about piecing together information, not about finding information. Make discovery easy; interpretation challenging.

📚 Further Reading

Learn more about investigation design: