In Ye Booke of Tentacles IV, Sandy Petersen presented an article, “the Lazy Man’s Guide to Creating Call of Cthulhu Adventures. It is a small article, and if you can find a copy of it, I highly recommend it. I found it at Yog-Sothoth.com a few years back, but a recent perusal did not bring it up, I am unsure of its availability, though I recommend finding it if you can. A simple means of using short summaries of films or novels as a starting point and how to take it and ‘run with it’ is presented, and is a good means for creating scenarios.
In YouTube, you will find many videos of varying length and quality, I found two to be pretty good.
The first is more critiquing the linear nature of published scenarios to his experience (a point I do agree with, in a lot of cases, though I think a good Keeper can work with and around this in most cases, depending on how extremely linear the scenario is built) for a large chunk of his video, his other points are very good, which leads to one of my other recommendations later in this post. This one brings up an excellent point, and how he lays it out is worth paying attention to, particularly when you are creating an ‘event driven’ scenario. A time frame is a component often neglected in how a scenario may be written, and the exceptions to this do tend to shine a bit because of it. The title for this video is RPG Discussion: Writing Call of Cthulhu Investigations, posted by Wolf3118, and the link is as follows, it runs just over eight minutes. http://www.youtube.com/watch?v=hv9Ye3UDMgk
The second is one in a series called Dm’s Tips, I specifically point out episode 37 Story Boarding 101, by Sean Connors. This series I am still working through, but I have found them to be universally good for scenario construction for any rpg, this particular episode is on the topic of storyboarding and focuses on a Call of Cthulhu scenario. This technique is particularly good at creating a non linear scenario structure, which anyone whose read this far knows is an issue I have with CoC scenarios. The less linear the better. I have found that in my own scenario construction, this is a very handy (read important) tool to add to the kit, and I also find that when converting a published scenario to fit into a campaign or one shot I will be Keeper for, storyboarding it helps me deal with any reservations I may have with it and bring it into a focus more appropriate for my gaming style. (I actually will do a post about my own storyboarding style soon, but it uses this principle as a basic starting point.) the url for this video is http://www.youtube.com/watch?v=ProvmFdEkLQ
The supplements I’m recommending, the first is a web page. A Keeper can use this page to springboard entire campaigns easily with this page alone. Starting as an article in the Pagan Publishing magazine the Unspeakable Oath, Steve Hatherley presented us with these Tales. Each one is a story seed, a brief summary of a story hook/opening. Then three possible interpretations are presented, and of course, this also encourages the Keeper to think of their own as well. I have not been to the page in some time, it looks like it hasn’t updated for a while, and navigating it isn’t as easy as it used to be, I’m having trouble finding an exact core index page so far, but if you do get into it, you will find literally hundreds of seeds worth tinkering with. the home page is http://www.talesofterror.net/ and with a little work with it and Google, I have no doubt you can find it. I have been able to find at least one of the sub pages, so I stand by this recommendation.
The second and third recommendations are sources for somewhat random structures, so there may need to be some tinkering to make them work right, and in both cases, fleshing out after them falls to the Keeper, so it’s not a ‘pre fab scenario’ source. The first of these is available as a pdf at Yog-Sothoth.com, in the Files/Utilities & Guides section. This is a document that allows one to randomly generate the skeleton and population of a scenario. It was designed for the d20 version of Call of Ctulhu, so an additional conversion may be necessary in a few spots.
The next recommendation is sadly out of print, but worth tracking down on Amazon or Ebay if you can. Gary Gygax’s Insidiae is another random adventure generator, a book that is geared towards fantasy games, but can still be applied to the Call of Cthulhu framework. Again, this needs fleshing out and application, but is an excellent resource.
The fourth one was hinted at in Wolf3118’s Youtube video, and upon reflection, is worth a read if one is stuck or wanting to get into world and adventure building mode on a base level. The Dungeons and Dragons 3.5 Edition Dungeon Master’s Guide is largely devoted to the concept of scenario building, pretty much from the ground up. You still need to convert concepts from fantasy to horror, and the DMG obviously is geared for its gaming system, but the ideas are valid. Granted, you aren’t having to build the world from the ground up, but there is a lot of room to change your setting world that this can help with. To be honest, this is not the best specific tool for CoC scenario building, but it can be useful for a ‘jump start’.