The Moonstone Affair

Outline of the Campaign

The Moonstone Affair is a free-form, investigative campaign where the investigators initially tries to solve a murder, but later desperately tries to save their sanity.

The campaign is inspired by the noir genre, huge campaigns as Masks of Nyarlathotep and a conviction that an adventure should allow great freedom of the protagonists to investigate things in any order. And of course; everything shall have layers as an onion—nothing should be like it seems!

This means that The Moonstone Affair can be played as a very short adventure, or be morphed into a long campaign. Due to this, the Affair will be referred henceforth as either by name or as “the campaign.” A long campaign is assumed and Keepers that want to keep it short will need to cut things to size.

The campaign is divided in a few scenarios or story arcs, each one can be investigated to its ends before the next is started or they can intertwine and be solved in parallel. In the latter case it will be more daunting and confusing for the players (and not only the investigators), but they will probably not run every red herring to the ground either and not get sidetracked by the smoke and mirrors the antagonists has deployed. Each scenario is divided in a number of “scenes.” The scenes are all described in detail, and usually with some additional information about what will happen depending on what other scenes has been visited before, but the scenarios will hold little information about in what order the scenes comes. The same applies for the campaign, albeit there is a red thread through the scenarios, the campaign does not define in which order the scenarios shall be played. It is the decisions and actions of the investigators that defines the order of the scenarios; The Moonstone Affair is as far from a railroaded adventure as you can possibly come!

Structure of the material

The material consists of scenarios, NPCs and places of interest, and some additional texts and explanations. It is organised as a wiki, not as a traditional book. Under Time line of the campaign below, a list of scenarios can be found and the expected order of them. Everything starts with the scenairo A murder is discovered, and then it is very much up to the investigators what happens next. A good place for the Keeper to start is to read about What acctually happened, and then continue according to the Table of Contents, but do use the keywords index heavily and the list of dramatis personæ.


I published my Fate of Cthulhu on 18th April, 2018, while Evil Hat published their at 13th January, 2020.

The scenario is written with two sets of rules in mind; Call of Cthulhu and Fate of Cthulhu. The latter can be found at Gamemaster’s Refuge and is not to be confused with Evil Hat’s Fate of Cthulhu, which came later!

Philosophy of the campaign design

As has been outlined above, there is no fixed order of the scenarios or the scenes, but to avoid total chaos the following order has been presumed in the writing of the campaign.

Off course, complete freedom is not possible as the investigators cannot accuse someone for a murder that has not been discovered yet. To sort out the impossible story arcs are left to the Keeper to do, the author of this campaign cannot predict how every and each player and player group will respond to the threats to their (investigator’s) sanity…

The campaign has been designed with a similar take on investigation as The GUMSHOE System; vital clues should not be missed because the investigators doesn’t look in the wrong place or the player unwittingly rolls the dice that has depleted all their low rolls and now only will roll high numbers to even out the statistical randomness and keep the universe in balance.

This means that most of the clues are described in scenes that are deliberately undecided on where they are located geographically and temporarily. If the investigators are in the right place at the right time; let that trigger the scene and let them have the clue. If they can make something out of the clue or not it is up to them, or if they even consider the clue to be a red herring.

Time line of the campaign

The campaign is assumed to start on the Wednesday, 13th of October 1928, there is nothing special with this date but selected on random. A larger US city is assumed, e.g. Boston, Los Angeles, Chicago or similar sized city, but London, Stockholm, Berlin, or Venice are equally usable.

Scenarios that gives important clues and/or are central to the campaign are marked with .

  1. A murder is discovered
    1. This forms the start of the campaign.
    2. How the investigators gets involved and why they start to investigate the murder is left to the Keeper and the players to decide. It depends so very much on so many different factors, e.g. new investigators or experienced ones from a previous campaign or the professions and backgrounds of the investigators, so it is not possible to give nothing but very simple suggestions.
  2. A Burglary in the Night: The main clue this event might give is the possibility for them to notice and get interested in Corien Cogh.
  3. A Dog is Buried: The first major complication of the plot and an opportunity to early rope in several other interresting parties into the story.
  4. A Chase in the Night
  5. Strange Neighbours: In case the group doens’t think there is enough Mythos in the story…

Trail of Clues

It is quite difficult to connect all the clues to the various events, something that is explained in this chapter.

Overview of the Trail of Clues (click to enlarge)

Web of persons

Overview of the Web of Persons Clues (click to enlarge)

The scope of the campaign

The campaign is written with the pretext that the investigators shall solve the murder of Christin Barnett and Maurice Arteaga, locate the moonstone and decode the message. They probably will need to fight off the Cult of the Serpent People as well as the Chthonians’ cultists in the process. What happens then is slighty outside the scope of the campaign as it is written now, but there are some obvious options. They could take on the Chthonians who will move to the area to get hold of the moonstone, as well as a group of Serpent People. Finding clues to their whereabouts and findings methods of fighting them off (the likelihood that a puny human mind can contrive a trap that makes them fight each other off is slim, but maybe it is why they can succeed as neither race thinks the humans can be that clever?) can easily evolve into a grand campaign itself.

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