Warning: Wikipedia contains spoilers
While D-FENS (as he is known as for much of the film, by his car numberplate) makes his rampage through the city, a cop by the name of Prendergast (played by Robert Duvall), on his last day on the job and relegated to working behind a desk starts a search to apprehend him. On the way he picks up clues which single out D-FENS and we learn about both policeman and engineer as the film progresses; D-FENS has been recently downsized and divorced by his wife, losing custody of his daughter and his job. Prendergast has a mentally ill wife who forced him to stop working on the street and now wants him to move with her to Arizona.
As the film continues it becomes apparent that D-FENS thinks society is full of ignorant, selfish automata, that he can't identify with most people, and that the few people he can identify with don't want much to do with him. When he does arrive "home", his wife and daughter have gone, having fled to a pier.
BBFC Certificate: 18