This is a small setting supplement. Set in 1930s earth it is described as a showcase for some rules in GURPS Thaumatology - specifically Book/Path magic.
I am not a fan of the title as it really is a setting and I think those looking for a setting could easily overlook it. And those looking for a new magic system will be disappointed as its mostly a showcase for a system in GURPS Thaumatology. It has some nice tweeks but no new rituals or rules. I think the reason for the title was that you need GURPS Thaumatology to use it. Besides Book/Path it uses Spirit Assisted magic, Alchemy, and includes pulp type supers with magic as the primary origin.
The emphasis is on alchemy but Book/Path magic is treated well and both are important to what is mostly a secret magic setting. This us a classic pulp genre setting, it can be played locally or with world travel to exotic locations. GURPS Mysteries, GURPS Places of Mystery, and GURPS Cliffhangers would all be great companions to GMs of this setting.
I really found this a fun read and a good pulp setting.