Mages
Overview: Magic is a real force in The Dark Mod setting. Everyone believes in magic and most people interact with minor forms of magic on a regular basis. Mages are those individuals who, through intensive study, learn to harness great amounts of magical power.
Info: Most people with the ability to use magic only develop the skill to do fairly easy things, like using tea leaves to tell fortunes, healing minor aches and pains, or creating small wards against rats or disease. With a little knowledge of alchemy or herbalism, these people can create successful potions or amulets. These people are not considered Mages and are generally referred to as 'Hedge Wizards' by their more powerful cousins.
True Mages have greater magical ability, and through academic study have learned to do things like controlling the elements, or hurling balls of flame or ice. They can create illusions to mislead people or even conjure evil creatures. Most of these things are highly illegal, in The City, of course. Powerful magic like this requries huge amounts of energy and concentration. Any slight mistake by the Mage can result in the magic going awry, with unpredictable (and usually highly dangerous) results. Powerful magic is therefore rarely seen by most inhabitants of the city.
The Order: The Hermetic Order is a loose organization of Mages, headed by a Mage Council. This Council maintains its authority by maintaining complete control over arcane books in the Great Library. Only members of the Order are allowed access to these books, and without them a Mage cannot hope to improve their skills in any significant way. Copying or removing texts from the library is strictly prohibited so that the Council can retain their monopoly (they claim it is to ensure 'quality control' over magical texts and to guard against damage or theft).
If the Council learns of arcane texts in the city that are owned independently (foreign mages or those who have discovered them in ancient ruins), the owner (if a mage) is 'invited' to join the Order and turn over the text. If they refuse, they are blacklisted. If the owner is not a mage, then the book will be either purchased or confiscated, "for reasons of safety".
The Council has some political influence in the city. Nobles looking to hire wizards usually go to them first, and merchants know that donations to the library are good ways to get 'lucky breaks', like fair winds for their ships. The Council can also forbid Mages from working for a particular family, so if a noble offends the Council, they will find it difficult to hire a Mage.
The Council uses this political favour to protect its members from persecution by the Church, although they cannot do much openly. They have to walk a fine line between protecting their members and directly opposing the Church. The Council investigates any wizard who may be causing problems in the city, and any wizard who displeases the Council risks being turned over to the Church as 'an example'.
There are fewer than 50 registered Mages in the Hermetic Order (not counting apprentices). While many people are born with the talent to use magic, few of them achieve the knowledge and strength to pass the applications tests of the Order. They must also be taught the "Wizard's Tongue"--the special language that books of magic are written in to keep their secrets from outsiders.
When a wizard passes the application test, they become an official member of the Order, and are given a talismen to identify them. These talismans are magically bonded to the Mage and are used as their pass to the secret rooms in the library. A talisman could be a staff, an amulet, a ring, or something else significant to the mage.
The Council rarely keeps tabs on what other Mages are doing, investigating only if there is a serious complaint. As long as they don't draw unwanted attention to the Order (like working illegal magic in the open), and don't go against the rare edicts of the Council (like not working for a particular noble house), Mages are free to do what they like.
Magic in the City: According to Church law, it is illegal in the city to charge money for most magical services. Because there's such a demand for it, the Church can't just totally outlaw it, so they just make it very difficult for Mages to operate (like prostitution--it's not illegal to be one, it's just illegal to charge money for it). Of course, lots of Mages sell their services, but it has to be done 'under the table'. Mages either sell on the black market (to people like our thief) or they manage to get a wealthy patron who supports them in return for their 'wise counsel' (since they're getting paid only as an advisor, they are free to cast helpful spells for their patron on the side).
Certain kinds of magic are not only illegal, but they are considered evil and can result in the Mage being arrested by the Church as a heretic. Magic that tells the future, magic that manipulates the mind, or destroying property with magic are all bad. Obviously summoning demons or messing with the dead are also on that list. Other magic, like healing, summoning rain, and making magic lamps, etc, are ok, as long as you don't openly charge money for them.
Mages know that if they have a powerful patron who really values them, they are less likely to be charged with heresy by the Builders. These mages tend to dress in outlandish ways, carrying strange staves and advertising their status as a mage to all. The rich clothing is almost like political armour, informing those around them that they have enough political protection to be safe from Builder persecution. The less powerful the protection a mage has, the more conservatively they tend to dress in public.