A Shock to the System is:

• a novel by British author Simon Brett, first published in 1984.
• a U.S. film (1990) by Jan Egleson , based on Brett's book, starring Michael Caine, Swoosie Kurtz, Elizabeth McGovern, and Peter Riegert.

A Shock to the System is about a Briton named Graham Marshall (Caine in the film), a long-time executive in a large New York City advertising company who unexpectedly is passed over for promotion. While Marshall himself could live with it, his nagging wife (Kurtz) is devastated and continually reproaches her husband for his apparent lack of stamina and willpower.

An unfortunate accident on the underground (U.S.: subway) caused by Marshall in which a panhandler is killed, but which goes unnoticed, gives him a whole new set of ideas as far as his future life is concerned. Deciding to take revenge on all the people who have caused him problems in his life, Marshall starts meticulously planning their violent deaths. This includes his young rival at the office and his wife, whom he eventually electrocutes (hence the ambiguous title). When none of the murders is linked to him, Marshall feels confirmed in his belief that killing off everyone who has harmed him is the right thing to do and soon passes the point of no return. At the end of Brett's novel, however, overwhelming evidence is suddenly brought against him for a murder he did not commit.

This ending was first used by Anthony Berkeley writing as Francis Iles in his 1931 novel Malice Aforethought (see whodunnit). It should also be noted that the ending of the movie version is completely different, with Marshall exulting in his new life of crime and in no danger whatsoever of being brought to justice.

See Helen Zahavi 's novel Dirty Weekend (1991) for a story with a similar subject matter.