I am beginning to work on laying the groundwork for the next story arc dealing whit the cult of mercury. I am looking for more info on them. or do have free reign to do what I want with it outside of dealing with ritual magic?
There are a few bits around them in different places, some of which is mutually inconsistent.
- Houses of Hermes: True Lineages (pg 95, 96, 99, 100) introduces the cult and its mastery abilities, and has a bit about cult practices. There's also a possibly-sub-cult known as the Cult of Heroes described here.
- Houses of Hermes: Societates (pg 16-17) describes the cult from a Flambeau perspective and has more about the culture of the Cult.
- The Mysteries: Revised Edition has a chapter on Mercurian Magic. In it it makes clear that the Cult of Mercury does not itself practice initiations, but there is another group, the Neo-Mercurians, who do initiate Mercurian style magics.
- Faith and Flame: The Provencal tribunal has a bit on the local version of the Cult (pg 28), including a covenant, Aedes Mercury (pg 83), which acts as one of its major centres. They have a mystery initiation for Mercurian Magic.
- Mythic Locations: One of the locations is a temple of the original roman Cult of Mercury.
There is more than one Cult of Mercury. Not only the neo-mercurians, I think, but more than one non-neo cult as well. This, of course, explains the inconsistencies that @Salutor refers to.
None of the canon cults are fully defined. Thus you have to make your own way. The citations that @Salutor gives are good starting points only. You can do with just one though, and assume that all the others are splinter cults ...
Ok, that is nice to know that gives me a lot of freedom to go where I want to with. Now I just hope THis game lasts long enough to see it to the end.