The lost son (1999)

Xavier Lombard is a world-weary private eye in London, in exile from his native Paris; his best friend is Nathalie, a high-class call girl. He gets a call from an old friend from the Paris police department, now a businessman whose brother-in-law is missing. The missing man's parents hire Xavier over their daughter's objections, and quickly he finds himself in the realm of children's sexual slavery.