Part I    My name is Mark, and I was divorced for 5 years and 43 years old when I first met Karen, the woman who was later to become my second wife. From that new relationship a temptation and obsession unlike any I have ever had presented itself to me.  That took the form of her daughter from her first marriage, Rebecca, who was fifteen years old when I first laid eyes on her.  Rebecca was heart-stoppingly beautiful:  be...