The book itself is small, only about 72 pages, but really that is plenty for the topic. You need the latest version of the Basic Role-Playing System book from Chaosium since there is no character creation information in this book.
We are given an introduction to witches and witchcraft and how they can fit into various game settings from Dark Ages to High Medieval to High Fantasy and Arabian Nights and Renaissance. What is mission of course is a Modern setting, but I think that might be assumed, given the nature of the BRP rules.
Caveat: It has been years since I have played any BRP game. I have the newest BRP rules set and I like them a lot, they are just far down on my list of go to games.
The nest section details the Witch Profession.
As a conceit of the monograph the author decides that witchcraft is an oral tradition and thus does not use a grimoire. I can live with this for the time periods mentioned above, but a Victorian age could, and a Modern age witch would most likely be literate and keep a Book of Shadows. This is only a minor quibble though.
There are skills detailed some new, others expanded.
Spirits or Demons details where a witch gets her power. I like this distinction since it gives a variety of types of witches; From your devil-bound or demon worshipping evil witch to the pagan or natural earth witch. To borrow an analogy it is roughly the same distinction made in the Rachel Morgan books by Kim Harrison. Earth magic would be this book's Pagan, Ley Line would be Neutral and Demonic is Infernal.
Given the history of the BRP game and taking a page from D&D4 it would not be difficult to imagine a "Mythos Witch" that gets her power much like the Infernal, only from the Lovecraftian beasties. With loss of SAN of course.
Coven and Sabbats cover the organizations a witch can belong to; Family groups, to supernatural ones to solitaries. Each of these can be expanded into various examples. The family groups could be something like Ann Rice's Mayfair witches or gypsy folk magic handed down mother to daughter.
The section on Witch's Magic is the meatiest. There is a mechanic for dealing with an oral tradition based magic system. It is nice and I like it for it simplicity and it's general common sense logic. It just looks like it works. Alterations for Familiars are mentioned as well.
There are a few new spells, but oddly enough I did not see one for Blindness, a rather iconic witch maleficia. But all look fine and fit the background material well.
In addition to spells we have new Witch's Sorceries and Witch's Potions.
I like the potion section the best of these last three since it is difficult to find good rules for witches making potions on the fly. In D&D 3 it takes way too long, but if you watch shows like Charmed or read books like the Dresden Files or the Rachel Morgan series their witches are brewing potions in hours, not weeks. Like the spells there is a good number of effects listed here. We also get Talisnans.
In Witches' Allegiance we see the differences between white and black magic and what the character gains (and looses) for their allegiance.
Mystic Artifacts details some of the unique magic items that are connected to witchcraft, Baba Yaga's Hut, the Hand of Glory and a couple of others. I would have liked to have seen Circe's Wand too, but that is just me.
There are some Sample Organizations which are flexible enough to work in any game really.
And finally we end with a number of Witch NPC Sample Characters.
This is a good book and if you want to play a witch in one of the BRP games then this is a great place to start. I could see these, as written, working in a Call of Cthulhu game or even an Elric one.
The book itself reminds me of the old Mayfair Games book on Witches for 1st Ed. AD&D. The tone and tenor is the same and there is plenty of text given to both sides of the witch persona; the good and the evil.
In terms of "playing a witch" I think this is the closest thing you can get in a BRP game. The author has clearly done his research and I am certain he knows there is so much more that he could have written.
I suppose the only issue I had with it was the lack of support for playing a modern age witch. Not that I don't already have a 1,000 games now that allow me to do that, I found their exclusion odd.
All in all I found this book to be an enjoyable read and looking forward to stating up a few witches using it.