The Need for Reread
So I am rereading the Swords of the Serpentine playlets materials and seeing all the mistakes I and players made. Although I have always added story flesh onto the bones of the rules, when I run older games, incorporating the rules encouraging story in Gumshoe games take some getting used to.
To help me conceptualize all this, I'm going to give a stab at making some simple story rules for Call of Cthulhu, probably my most played and run game, based on the Gumshoe concept of Investigative Abilities.
Investigative Abilities for Call of Cthulhu
First, the Occupation of each player character serves to define their Investigative Ability (IA). An IA lets you get free clues and leads if reasonable for your character to do so, and by using attribute ratings as a pool of points, you can buy special, story effects. Note that using a pool point does NOT reduce the attribute, just how many pool points can be used. Points replenish when the adventure ends, or a major menace is defeated.
Players must give reasonable or interesting rationales for their pool spends. The strength of effects depends on how many points are spent. Here is a rule of thumb (something which I thought SotS sorely needed):
1 point spend: affects the scene
2 points spend: affects the character
3 points spend: affects the setting or NPCs
4 points spend: affects the game world
For instance, two characters, Paul the Policeman and Anne the Antiquarian, are on an adventure together trying to infiltrate a cult of Dagon worshippers.
Paul will automatically know that a homeless person found dead in the street was killed by cultists when he sees the corpse.
Additionally, he can spend 1 point of Intelligence, Education, Power, Appearance or to know common criminal lingo to be allowed in the door when he wants to bluff his way into their hideout.
He may spend 2 points of Power of Appearance to have an incredible resemblance to the cult leader (which the Keeper may use against him later in a reveal of family connection).
During the climatic battle when they are outnumbered, he can spend 3 points of Power or Appearance to establish a rival group of monster-hunters exist to help them fight.
Finally, he can spend 4 points of Power or Appearance to make all fishermen automatically have knowledge of the cult and ways to defeat their magics.
Similarly, Anne will automatically what tome a certain spell is from, and what language a book is written in, even if she cannot read it herself.
She can spend a point of Intelligence to remember the tunnelled over entrance into the back of a building they wish to enter secretly.
She can spend 2 points of Power to know a spell summoning a magical mist that lets them sneak away when in a pinch.
She can spend 3 points of Appearance to know a bookseller who lets them access his collection for important research.
Finally, with 4 points in Power she can insist that Poseidon exists and is an Elder God who opposes Dagon and helps those who do so when in peril.
Finally, players can also use their character descriptions to get bonuses to rolls. For every point spent, characters can get +1d6 to damage, 1d6 armour to soak damage, or +20% to a skill roll, or an automatic success for a roll.
Note that these IA may seem overpowered at first glance. However, when you recall that the Keeper has endless resources to throw at PCs, incorporating Investigative Abilities and their story effects constitute a type of false hope that fits well with Lovecraftean cosmic horror, while allowing the sometimes stead mechanics of CoC to better replicate the weirdness and coincidence of the fiction that inspired it.