Most Investigators are accustomed to having, in the course of their investigations, to consult the odd musty tome in the library - but have they ever wondered how they got there? The core idea of Bookhounds of London is that the party consists of book-dealers who hunt down and sell said dusty old tomes, and get dragged into dealing with what some of them cover almost by accident...

The first section, Bookhounds, is all about creating appropriate characters from somewhere in the rarified yet disreputable book-dealing world. (OK, I know it's set later and is about the Devil rather than the Mythos, but the movie The Ninth Gate keepts floating around my mind at the moment.) There are some new occupations directly engaged with the rare book trade as well as suggestions about how to twist existing ones to suit. There's also a fascinating new Ability called The Knowledge, which - similar to a London black cab driver - confers an encycopaedic knowledge of what's to be found in London and the best route to get there.

Next, a look at Bookshops. The idea is that all Bookhounds (which is what Investigators are called in this campaign) are based in and around a store, run by one of them who has taken the Bookseller occupation. There are various rules for defining stock and other such matters (if you want to go into so much detail) but the real purpose of the bookshop is as a focal point for adventures and a home base for the Bookhounds themselves. Various types are discussed, from a book-barrow under Waterloo Bridge to fancy high-end stores and high-end auction houses.

Appropriately, the next section is The Purchase of Curious Tomes. While the book trade itself is important in this type of campaign, it's not central and some groups may wish to keep it more in the background than others. The rules here enable the simulation of a thriving book store's operations without bogging down in too much detail, and there's enough terminology to make you all sound the part. For those too young to remember 'old' British money, a complex system ditched in 1971 in favour of the decimal system in use today, there are notes on that, although it's suggested that you abstract rather than getting too bogged down in your pounds, shillings and pence. Estate sales, auctions... complete with dramatic rules for auctions when you want to play one out.

Next come Libraries. The sort we are interested in here don't lend, you have to go there - and be allowed in - if you wish to consult their books. Even when you have gained admittance, the sort of books that interest us here may be on restricted access. Several suitable libraries in London are described, with notes on how to get in and the books to be found there... and then of course we have the Books Themselves, beginning with physical details and then moving on to notes on the different kinds of occult works to be found. Sample genuine historical occult books are listed for some local colour, before moving on to Mythos Tomes with again a few examples.

We then leave the books aside, with a massive section on Thirties London. There's loads of flavour text to help you get a feel of it, with rumours and contacts galore. Different sections of London are outlined, and it makes for a fascinating read never mind a useful resource. The survey is followed by a section on The London Mythos which discusses cults and individuals, complete with plot hooks and other notes to get them mixed up in the stories that you have to tell. Many call upon monsters, so the next section is London's Monsters. Each comes with copious notes to make them easy to use when the need arises.

Then comes the strange magick of Megapolisomancy. This weird art uses the city itself to cause change to occur in accordance with will - it may be something you can study like other arcane arts or perhaps it is used insinctively by those steeped in a city's lore. The extensive material here will let you incorporate it into your game: whether you let the party use it or reserve it for NPCs is up to you.

Now to practical matters with a section on Running a Bookhounds Campaign. There are plenty of styles to conjure with here, read through and decide what will suit the group and the stories you have to tell best. Ideas about, enough to spawn several campaigns... and that's before we reach the NPCs. There are example bookstores, complete with owners, staff and their own bookhounds, as well as individuals of interest. Even if you don't want to run a Bookhounds campaign, these could come in useful if more regular Investigators want to interact with them during the course of their adventures. These NPCs come with a range of options, shaded to suit the style and needs of your campaign: customise them to your heart's content.

The discussion then moves on to Scenarios. Like any other for this game, they provide a series of encounters and clues that lead to an horrifying glimpse of the Mythos lurking just beyond the ken of normal folk, occult mysteries revealed. Structure and pacing are discussed, mechanical tools that if used during the design process ensure that the whole thing stays on track and delivers suitable horror-laced entertainment to your group. Use maps liberally to give a feeling of location and with liberal use of plot hooks, character-driven adventures, and contacts you will soon be up and running. As an example, there's a whole adventure, Whitechapel Black-Letter, to get you going. There may be a book at its core, but this scenario provides scope for plenty of action as well!

Appropriately for a book about books, there is an extensive bibliography in back, along with some floorplans. Perhaps the Mythos is loose in the Palace of Westminster (home of the British Parliament), or there are clues to be found in the National Gallery, the Natural History Museum or even London Zoological Gardens. The Tower of London, the Victoria and Albert Museum (the Vic and Al, as it's known to locals) or the British Museum itself might contain that for which you seek. There are plenty more maps as well, street maps of most of London (I can even find the street where I grew up!), plenty for your group to explore. Various forms and appendices round this work off.

Not only does this provide a very novel slant to adventuring, there's the tremendous resource of London laid out for you whatever you want to do there, and an inside look at the book trade that provides the tomes your Investigators (be they Bookhounds or not) find themselves pouring over. And there's a cracking adventure to boot!