After a body is found in the walls of a French monastery, Commissaire de police Niemans, played by Jean Reno, teams up with Detective Reda, played by Benoit Magimel, who is already investigating a murder of his own. As with the first movie, the pair's investigations intertwine and soon they are looking at a giant conspiracy involving a secretive group of monks on amphetamines led by Heinrich von Garten, played by Christopher Lee, searching for a treasure hidden by King Lothair II somewhere near the Maginot Line. Reno and Magimel are joined by a religious specialist called Marie, played by Camille Natta.