How to Write a Call of Cthulhu Scenario

Design process, not Mythos trivia

This is not a rules course

It’s not Mythos lore either.

It’s what a Keeper actually does to turn an idea into a runnable scenario.

Five decisions, in order

  1. Premise — a spark, made specific
  2. Truth & antagonist — what actually happened, and why
  3. Structure — linear or open, committed to early
  4. Clues, puzzles, checks, NPCs — built to survive a bad roll
  5. Playtest & assembly — tested on someone else, handed to someone else

The scenario isn’t finished when it reads well. It’s finished when someone else can run it.

Where this comes from

  • the convenor’s own scenario-writing practice, week by week
  • checked against Chaosium’s own Keeper-craft guidance, Blase’s clue framework, and Petersen’s Alexandrian model
  • where they disagree, the course teaches both and says so

This semester

  • weeks 2–5: premise → truth → structure → scenes
  • weeks 6–9: clues → puzzles → checks → NPCs
  • weeks 10–12: atmosphere → playtest → assembly

Four assessments track the same arc — pitch, architecture, playtest report, final scenario.