The Sicilian Method By Andrea Camilleri

(Commissario Montalbano #26 )

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Mimi Augello is visiting his lover when the woman's husband unexpectedly returns to the apartment; he climbs out the window and into the downstairs apartment, but one danger leads to another. In the dark he sees a body lying on the bed. Shortly after, another body is found, and the victim is Carmelo Catalanotti, a director of bourgeois dramas with a harsh reputation for the acting method he developed for his actors. 

Are the two deaths connected? Catalanotti scrupulously kept notes and comments on all the actors he worked with, as well as strange notebooks full of figures and dates and names. Inspector Montalbano finds all of Catalanotti's dossiers and plays, the notes on the characters, and the notes on his last drama, Dangerous Turn--the theater is where he'll find the answer.