In 1950s, New Orleans, where the Mardi Gras festival is in full swing. Thanks to Weekly, a jazz producer named Faust meets Blacksad. Faust asks him to take care of a case: one of his musicians, pianist Sebastian, has disappeared. He hasn't given a sign of life in months, endangering the private musical label of a star. Faust fears that Sebastian has, once too much, sank into drugs. His request is all the more pressing as Faust knows himself is suffering from cancer. John accepts the mission and gradually discovers that Faust hasn't told him everything. He sees that he is himself manipulated, but decides to find Sebastian to understand the reasons for his disappearance. He doesn't yet know that he will know his most trying investigation, in more than one respect.