Unasked for suggestions
Because I can't let these kinds of things go, how about...
The PCs are a band of book thieves and forgers (possibly all of whom have legitimate careers in the literary or academic world) who, several years ago, worked together to steal and replicate a french grimoire that dates back to the 1400s. They replaced the copy they stole with a fake and sold the original to a private collector.
The fake recently went up for auction and was purchased by a book agent working for an unamed patron. A few weeks later the agent was found dead in her hotel room with no obvious clues as to how or why, except a strange symbol drawn on her forehead. All of which would be meaningless to the PCs except that the same thing has happened to the private collector to whom they sold the original, a man reported to have mob connections.
Meanwhile the PCs are being investigated, or harrased, by various agencies that could include the FBI, Interpol, the CIA, and assorted mafia types. All of whom have apperantly picked up the connection between the book and the PCs, or at least suspect it, and want to know what is going on. Thus the PCs are drawn together again to protect themselves, to either solve the mystery or wind up in jail or dead. Add to this mysterious letters from different hands either threating, pleading, or courting the PCs to come forward with any information about the book, strange symbols showing up in odd places, long time friends and coworkers asking unusual questions, and the sense of wings fluttering on the edge of vision over and over and you have a sufficently occult/conspiracy/crime adventure that could take the PCs anywhere in the world and could be set in almost any time or palce in the last 200 years.