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Cardano Grille RPG Plot Generator

Saturday, February 17th, 2024

Had an idea for a plot generator for table top role-playing games last night. Probably best suited to an espionage or conspiracy theory game or a game set during the Renaissance. I was originally thinking of The Dee Sanction but Project Cassandra, Spy Master, Conspiracy X, Night’s Black Agents, 7th Sea and All for One: Régime Diabolique all fit the feel as do (I’m sure) many more I’ve not named.

Cardano Grille is a steganography cipher developed by  Girolamo Cardano in 1550. It consists of a Grille with holes in it that can be placed over a letter to reveal a concealed message. Wikipedia has a write up of the Cardano Grille‘s history and method.

What you will need:

  • A printer to print a grid
  • A craft knife to cut out some squares
  • A table of things to look up
  • A book to do the looking up in
  • A message template

Making a Grille

To make a Grille I printed a simple grid on a sheet of paper – card would probably be better for use at the table but for a prototype it was fine.

I used a 7 by 15 grid.

I cut a number of the cells out.

Cardano Grille prototype with a copy of The Complete Plays of Christopher Marlowe

Using at the table

As a plot generator for a tabletop RPG:

  • Take a Grille and place it over a page in the book – any orientation can be used
  • Read the first full letter in each of the holes
  • Look up what each of those letters mean and slot them into a message template

Example for a Modern Spy Game

Message Template:

There will be an [Letter 1: Incident] in [Letter 2: Place] involving [Letter 3: Person] which you should prevent. Secondary Mission: If possible retrieve [Letter 4: Thing] from [Letter 5: Agency] who are [Letter 6: Incident] [Letter 3: Person].

Look up Table:

Letter Incident Place Person Thing Agency
A Blackmail Berlin Religious Leader Artwork CIA
B Provocateur New Orleans Police Officer Box DEA
C Brush Pass Shanghai Scientist Weapon GCHQ
D Compromise Tokyo Criminal Jewellery FSB
E Assassinate London Head of State Briefcase MI6
F Reconnaissance Nassau General Diary DHS
G Poison Amsterdam Expert Device DIA
H Defect Athens Agent Provocateur Artefact Special Branch
I Discredit Paris Agent Report GRU
J Wet Job Budapest Civil Servant Disc GIS
K Mole Cairo Spymaster Nuclear Device BND
L Black Propaganda Venice Diplomat Prototype DGSE
M Disinformation Kingston Computer Programmer Vehicle NIS
N Surveillance Rome Model Bomb Mossad
O Exfiltrate Washington Controller Cipher NSA
P Dangle Bern Actor Document SSA
Q Interrogate Sofia Cobbler Seeds GRLS
R Corrupt Moscow Business Leader Jewel KGB
S Honeytrap Istanbul Journalist Plans DGSI
T Black Bag Job New York Assassin Database FBI
U Kidnap Beijing Child Sample DIS
V Rolled-up Tirana Accountant Money SIS
W Transport Stockholm Femme Fatale Recording FID
X Sleeper Oslo Gangster Stamps DRM
Y Steal San Francisco Double Agent Microfilm USSS
Z Walk in Hong Kong Gang Member Passports DGI

Opening “The Complete Plays of Christopher Marlowe” at page 441 and placing the Grille over the page I got the following letters:

A, O, D, O, S, H

This gives the message:

There will be an Blackmail in Washington involving Criminal which you should prevent. Secondary Mission: If possible retrieve Cipher from DGSI who are Agent Provocateur Criminal

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