The Colletta Cassettes - Bruno Noble

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It's the summer of  '78 and 16 year-old Sebastian arrives with his parents and brother in the medieval Italian village of Colletta for a holiday.  
 
His father, an investigative journalist, has taken the family there with no explanation and is then only flittingly glimpsed in the company of a strange American. 
 
Bored, and tired of being treated like a child, Sebastian notices a young woman who sets his heart alight.  However, whenever he tries to approach Rosetta, he finds she is not alone. 
 
Older men carrying pocket knives skulk in the backstreets of Colletta, and the American is usually never too far behind. 
 
Who is Rosetta?  And what is her connection to sinister events in an otherwise picturesque village?