So you want to write a mystery novel? There is a really simple formula making the rounds now.
Betsy, the heroine (yes it is always a she) just moved to a small town from the big city, leaving her jilted lover behind. He will harass her at some future point by interrupting her new love affair and/or attacking her verbally and/or physically. He will leave in disgrace, having repented and finally seeing the error of his ways.
You might recognize this saying, a feather in your cap, or you may have never heard the term.
Meaning of the Idiom
According to the Oxford Dictionary of Idioms, a “feather in your cap” came from the late 17th century and originally meant a sign of foolishness