The Turn of the Screw (opera)
The opera is divided into two acts.  It is further divided into a prologue and sixteen scenes.  Before each scene starts we hear a variation on the 'Screw' theme.  This theme is based on twelve notes which are all the 12 notes in the octave.  This is called twelve-tone row, but it is tonally based (the music is in traditional keys, unlike the music of Schoenberg).  There are only 13 players in the orchestra.