In, say, the year 1984 (to pick a year at random), plagiarist Joe Schmoe wrote a novel and the opening line was "It was a dark and stormy night."
Now, when a 21st century author used that same line as the opening of a chapter in a best-selling novel, Joe Schmoe sued for damages, saying he owned the copyright and that he had registered the copyright when he published his book in 1984.
All the shenanigans involved in the legal case, and delving into the history of the sentence at issue could be fun to write. Such a story would almost certainly require colorful characters.