This is a work/idea in progress and may fall flat on its face, but let's see if there's interest:
Earth is mostly unchanged in the early-21st century. The big differences are that genetic engineering is highly advanced, magic exists, and supernatural beings are known. The Underground is an illicit brothel owned by a nebulous criminal organization. It specializes in exotics—fantasy races, anthros, sci-fi races—and has its own bio-thaum labs located elsewhere in the city. The underground is located in Dark City, a large fictional city on the middle of the American east coast. The city is pretty much avoided by the FBI, DEA, and other national, and state, law enforcement because it is effectively controlled by supernatural and magician led organized crime. So far at least.
Some Notable Groups
Collegium Arcanum of Northumberland—Basically a school for magicians of various sorts, located in northern England.
Syndicate, The—Supernatural alliance whose goal is the creation of a supernatural state and perhaps even a supernatural dominated world.
Gibson Institute—A research institute devoted to helping humanity through genetic engineering. Located in California.
Interpol Unit 5—International police unit focused on supernatural criminals and crime.
Supernatural Containment Command (SCC)—a.k.a. S-Cops; basically a specialized SWAT-style organization on the national level with training equivalent to a hybrid of LAPD SWAT and USA Delta Force. Designed to neutralize criminal supernaturals; equipped with top line mil-grade hardware including some “near future” gear unavailable to the general public. U.S. based.
Ok, very brief info up there. There's more specific info on The Underground (an illicit brothel in Dark City). That's all good to go as far as a group game goes. However, for the last couple days I've been toying with the idea of running two or three things simultaneously in the same setting: 1) at the Underground [in Dark City], 2) at the Collegium Arcanum [which needs some development in that case; in the U.K.], and possibly 3) an SCC or Interpol 5 based thing [probably somewhere in the U.S. but not Dark City]. With players certainly allowed to have multiple characters in one/both/all three.