When Gregory Crowne is enlisted to help Gilles Guidon, eccentric son of a merchant banker, to assemble a jazz quintet for the Montreux Festival, he soon discovers that there is something wrong at the Banque Guidon. Then Gilles falls hopelessly in love with Morena, the sister of one of the quintet, against strong opposition from his family, and his ancient nurse, Nou-nou, dies in a mysterious fall. When Gilles disappears with Morena, things soon become even more complicated, as a ransom demand arrives not for money, but for the password to an account at the Banque Guidon. Not only must Gregory figure out the connection between these events, but he has his own problems to deal with, as his relationship with Liz Blair becomes increasingly fiery.