Vicious Circles - Carolyn Lowery 1997

In a Paris cemetery, a handcuffed prisoner grieves at the grave of his sister Andy. In flashbacks, we see what happened. He's arrested for smuggling an Ecstacy-like drug; to get money to help him, Andy takes a job in a mysterious call-girl ring run by the wealthy and secretive March. She's goes to the American embassy for help as well, and she's assisted by Stanley Esher, a nerdy but competent bureaucrat. To train for the sex ring, Andy is taught by a blind masseur and advised by Helga, the friend who recruited her. There's also the drug, which can be stored in temporary tooth caps, released with a bite, and passed on with a kiss. Andy tries to outwit March, but the cemetery awaits.