Just saying...
http://en.wikipedia.org/wiki/A_Shock_to_the_System#Difference_between_book_and_film
Can't decide if it would improve the film or not. It's a very interesting twist in any case.
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A Shock to the System (1990) is a U.S. crime thriller film (...} based on the 1984 novel A Shock to the System by British author Simon Brett.
http://en.wikipedia.org/wiki/A_Shock_to_the_System
It is an interesting end to the book, though used in other novels and films, as it pointed out in the wiki article.
They did not mention another one that was the same as the book -- "The Return of Martin Guerre." An old French film that was remade as a Civil War film with Richerd Gere and Jodi Foster, which uses a similar polt device.