The unfinished final adventure of Tintin featuring Herge's black-and-white sketches

Opera singer Bianca Castafiore has a guru: Endaddine Akass is handing his advice out to everyone, but Tintin doesn't buy it--especially when he realizes that Akass might be connected to the death of the owner of an art gallery, who had been on his way to see Tintin when he died.