System

Call of Cthulhu is a d100-based game of cosmic horror and investigation that fundamentally inverts the power fantasy typical of systems like D&D or Pathfinder. Instead of playing mighty heroes destined to slay dragons and ascend to demigod status, you play as “Investigators”—ordinary people like librarians, private detectives, or professors—who stumble upon truths humanity was never meant to know. The core loop prioritizes atmosphere, research, and deduction over combat; you aren’t kicking down doors to loot the room, you are piecing together fragmented clues to stop an eldritch ritual, often while frantically looking for the nearest exit. It is a game where knowledge is dangerous, and the entities you face are not monsters to be farmed for XP, but incomprehensible forces that view humanity as insignificant dust.

Mechanically, the game is grounded, lethal, and defined by the erosion of your character’s resilience rather than its accumulation. Using the intuitive Basic Roleplaying (BRP) percentile system, you will find that combat is realistic and terrifyingly fast; a single gunshot can easily kill a character, encouraging players to treat violence as a desperate last resort. The game’s standout mechanic is Sanity, a resource that inevitably depletes as you witness the impossible or read forbidden tomes. In Call of Cthulhu, you generally don’t level up to become stronger; you slowly deteriorate in mind and body, striving to solve the mystery and delay the apocalypse before you end up in a sanitarium or a grave—a high-stakes dynamic that makes every survival story feel uniquely earned.

Intent

The intention would be to run stand alone scenarios that last a couple of sessions, mostly (but not entirely) in 1920’s USA, and preferably with prebuilt characters (but no problems with bringing your own!). Although there is a mix of investigation and outright horror, I’m biased towards investigation. Sometimes the ultimate horror is other humans.

The simplest candidates are scenarios that I have already run as part of my ongoing campaign, restored to their original locations and time periods!

  • Crimson Letters
    • Investigators in Arkham are hired to solve the bizarre death of a Miskatonic University professor and locate a sheaf of missing historical papers that disappeared from his office.
  • Spirit of Industry
    • Investigators become involved in rumours of the supernatural in an abandoned industrial town
  • The Nineteenth Hole
    • Investigators find themselves entangled in a baffling mystery at the local golf course
  • The Saturnine Chalice
    • Investigators are called to the rural English village of Tissington to investigate the disappearance of a young woman and the mysterious death of her father
  • Loki’s Gift
    • An investigation of a mysterious death. Was it suicide? Or something nefarious?
  • An Inner Call
    • Investigators must confront a radical philosopher named Wasserman who believes the Cthulhu Mythos is not an external threat but a psychological projection of humanity’s repressed, violent instincts that must be unleashed.

Here are some examples of potential scenarios that would be suitable for any group: