Breton longing

is asked to solve a mysterious death: a penniless Celtic musician washes up dead on the shore shortly before the most important festival of the year. The police discover a clue in his house that is linked to an ancient dark rite, but the remote island's close-knit community makes it difficult for Dupin to investigate - sirens, priestesses and storytellers live here outside the norms and know: It's the invisible that counts. And Dupin sets himself the almost impossible task of finding out what that might be.