As "Jean d'Enneris," Lupin finds himself engaged in a curious duel with his old opponent, Chief Inspector Béchoux. The Mélamare Mystery finds Lupin working both for and against the police-rather in his "Barnett" manner. But whereas in previous cases of the kind he has had no personal interest in the protagonists, this time he finds himself losing his heart to the delightful little mannequin, Arlette Mazolle. At once, the case is much more than an affair of missing diamonds. Lupin must solve the mystery, but in doing so, he must protect Arlette.