Although Chaosium have provided at least some support for the popular 1890s-based Cthulhu By Gaslight setting for Call of Cthulhu during the game’s 7th Edition era thanks to the Cthulhu Through the Ages supplement, which provides 7th Edition guidance for creating Investigators in a number of eras (and thus provides all you need to use existing Gaslight products with 7th Edition), until recently they hadn’t gotten around to fully updating the old Cthulhu By Gaslight supplement for the new version of the game. Originally put out in a couple of editions in the 1980s (a 1986 boxed set, and then a 1988 revision of the box contents into a softcover book), its most recent tune-up was back in 2012, a mere couple of years before the release of 7th Edition, and so perhaps it was deemed prudent not to render that redundant immediately lest it seem like a cash grab.

However, it’s been over a decade since that came out, so it’s hardly exploitative of Chaosium to put out a new version of the supplement – but rather than just take the old text, multiply all the core attributes by five, and move on (which is really all you need to do to convert a supplement from the 1st to 6th Editions of the game to 7th Edition), Chaosium have gone in for a root and branch revision and expansion that’s even more extensive than the job Kevin Ross did back in 2012 of expanding on William Barton’s original supplement.

This is sensible. The downside of writing an RPG supplement that’s about a real historical period is that on the one hand, you have the advantage of a mass of real-world material to base your research off, but you also have the downside that here in the Internet age a fairly sizable proportion of your audience has access to the same material. If you’re going to sell someone a supplement detailing a historical period, you’re going to need to something a bit more substantial than what they could get by skim-reading a few of the meatier Wikipedia articles on the subject; in effect, your audience is paying you to do the research legwork for them and present the material in a way which is of particular use for the purpose of playing in and running games set in the era.

This is particularly the case with the Cthulhu By Gaslight Investigators’ Guide – because the 7th Edition expansion of Gaslight is so major that it’s been split into two books. We’re promised that in due course a Cthulhu By Gaslight Keepers’ Guide will emerge giving NPC stats, Mythos threats, and other Keeper-facing rules and information; for obvious reasons, this is going to be where most of the outright fictional material is going to land. In contrast, the Investigators’ Guide is a player-facing book, providing a deep dive on the Victorian setting without spoilering any of the Keeper’s secrets – which in effect means that most of the real-world history researched for the supplement is going to end up here, because that history provides the pool of common general knowledge available to the characters in the setting, describes the zeitgeist they exist in, and gives details on the class and cultural context they hail from.

In fact, the Investigators’ Guide is rather cunningly developed so that it can serve as either a supplement or as a core rulebook depending on your preferences and what makes sense for your gaming table – rather than requiring Gaslight players who want a rulebook but don’t want any of the referee-facing stuff to get the 7th Edition Investigator Handbook, as you might for a game set in the 1920s (which the Handbook has a fairly extensive chapter on) or the modern day (which, since you reside there, you don’t need an introduction to), such a player can just get this book and have everything they need, because not only does this include the Gaslight-specific rules for creating an investigator, but it also has an appendix reproducing the basic Call of Cthulhu rules.

This, perhaps, might be a by-product of the development of the Call of Cthulhu Starter Set, since the condensed rules here are much like the brief version of the rules there – doing the exercise of seeing just how much you can strip down the rules and still give someone the details they need to fully participate in a game session seems to have helped Chaosium realise that they could put this out with a significant shift in the balance of setting material to rules stuff; whereas the Investigator Handbook has the full-fat rules explanations for players (and so may still be of some help to participants in Gaslight campaigns – if you already own it you didn’t waste your money) and about 40-odd pages of 1920s setting discussion, this book goes all-out on providing deep dives into the era.

This may be necessary. For one thing, the 1920s are increasingly in the rear view mirror, but they still feel more modern than the 1890s, and some players – especially those who haven’t studied 19th Century history previously all that much – may have less of a sense of what the era was like in general. For another, the assumed centre of gravity for Gaslight campaigns is London, due to the literary inspirations of the setting, and assuming everyone knows what Victorian-era British culture was like is a stretch. Thus the book provides an overview of British cultural values at the time and a deep dive on London, a close look at the rest of the UK, and sufficient details on the rest of the world to be getting on with. It also notes that the Down Darker Trails supplement can cross over with Gaslight, since after all the Old West is just an ocean liner voyage and a railway trip away.

When I reviewed the previous edition of the supplement, I noted that it didn’t go too deeply into some of the social inequities of the era, and tended to assume PC groups would be primarily middle-to-upper class. This version of the supplement realises that audiences these days won’t go for that, and so both provides guidance on how working class characters could contribute to investigations and provides a deeper look at the inequalities of the period – some groups will simply gloss over that, of course, but it’s better to have the information and not want it but to want it and not have it.

That isn’t to say it’s all dry sociological stuff. The section on Victorian occultism, in particular, gives a sense of the interpersonal drama and larger than life characters that existed at the time, and makes allusions to a system for astral projection detailed in the Keepers’ Guide – making me wonder whether they’re going to dip into the system for exploration of the astral plane (as imagined by occultists of the age) detailed in Pagan Publishing’s old, long out of print The Golden Dawn supplement or whether they’ve cooked up an all-new take on the concept.

On the whole, the sheer quantity and quality of the material in the Cthulhu By Gaslight Investigators’ Guide more than justifies the split into multiple books. After all, the core Keeper Rulebook for 7th Edition already gives you a toolkit of Mythos monsters and magic you can throw at your players, so if you want to start a campaign of the new Gaslight now you can have at it straight away with just the Investigators’ Guide with no need to wait for the Keepers’ Guide to come out, and then get the latter book once it’s out to get more Gaslight-specific material. (There’s also a range of useful third-party supplements for the era like Hudson & Brand.)

On top of that, the fact that all the Mythos-oriented, Keeper-facing stuff has been saved for the Keepers’ Guide means that the Investigators’ Guide is actually potentially useful for more than just Cthulhu By Gaslight. It’s kind of a backdoor generic rulebook for any Basic Roleplaying campaign that takes a detail-oriented approach to the Victorian era, and could also be a useful resource for exploring the era in any other RPG system. Lots of games have touched on the period, but few have managed it to the level of detail and clarity offered here.