The omega factor / Steve Berry.

The Ghent Altarpiece is the most violated work of art in the world. Thirteen times it has been vandalized, dismantled, or stolen. Why? What secrets does it hold? Enter UNESCO investigator, Nicholas Lee, who works for the United Nations' Cultural Liaison and Investigative Office (CLIO). Nick's job is to protect the world's cultural artifacts-- including countless lesser-known objects and national treasures. When Nick travels to Belgium for a visit with a woman from his past, he unwittingly stumbles onto the trail of a legendary panel from the Ghent Altarpiece, stolen in 1934 under cover of night and never seen since. Soon Nick is plunged into a bitter conflict, one that has been simmering for nearly two thousand years. On one side are the Maidens of Saint-Michael, les Vautours-- the Vultures-- a secret order of nuns and the guardians of a great truth. Pitted against them is the Vatican, which has wanted for centuries to both find and possess what the nuns guard. Because of Nick, the maidens have finally been exposed, their secret placed in dire jeopardy-- a vulnerability that the Vatican swiftly moves to exploit by utilizing an ambitious cardinal and a corrupt archbishop, both with agendas of their own.