The story involves a fake psychic, Blanche Tyler (played by Harris), and her con artist taxi driver boyfriend, George Lumley (played by Dern), who attempt to locate the nephew of a wealthy and guiltridden old woman, Julia Rainbird (played by Nesbitt). Julia, one of Blanche's clients, was responsible for her now-deceased sister giving up a boy for adoption years earlier and now wants to make him her heir. She will pay $10,000 if he is found.
However, the nephew and prospective heir is now a successful jeweler in San Francisco known as Arthur Adamson (played by Devane), who has a secret and lurid past, having apparently murdered his adoptive parents and faked his own death. With his girlfriend Fran (played by Black), he has successfully kidnapped an assortment of millionaires and dignitaries, returning them when the ransom, a valuable gemstone, has been delivered, which they hide in their chandelier.
When Arthur learns that Blanche and George are pursuing him, he suspects the worst, putting their lives in danger.
The novel on which the film is based had earlier been rejected by Ernest Lehman, to whom it had been submitted as a potential project for him to either produce and/or direct. Although Alfred Hitchcock and Ernest Lehman had attempted to work together on several projects following their huge success with North by Northwest, this was their only other project to be filmed. Lehman had incurred Hitchcock's anger by declining the offer to write the screenplay for No Bail For the 'Judge, a thriller set in London and meant to star Audrey Hepburn, Laurence Harvey and John Williams. Although Hitchcock eventually got a fine screenplay and preproduction, location scouting and costumes were well underway, that film was never made.
Hitchcock, who often liked to specify the locales of his films by using on-screen titles or by filming famous landmarks, deliberately left the story's location unspecific, using sites in both San Francisco and Los Angeles. The chase scene in the movie, which writer Donald Spoto called a spoof on car chases prevalent in films at the time, was filmed on the extensive Universal backlot. The restaurant used in the film was also built on the backlot and was shown on studio tours in 1975.
Alfred Hitchcock's cameo is a signature occurrence in most of his films. In Family Plot he can be seen (38 minutes into the film) in silhouette through the glass door of the Registrar of Births and Deaths.
The film was the only Hitchcock production to be scored by John Williams, a rising staff composer at Universal who had recently had a major career breakthrough when he scored Steven Spielberg's thriller Jaws, noted for its pulsating bass tones whenever the shark attacked.
Following Family Plot, Hitchcock worked on the script for a projected spy thriller, The Short Night. His declining health and eventual death in 1980 prevented the filming of the story, which was published in a book on Hitchcock's last years. Universal reportedly chose not to film the script with another director, although it did authorize sequels to Hitchcock's Psycho.
William Devane was Hitchcock's first choice for the role of nefarious jeweler Arthur Adamson, but Devane was unavailable when the film went into production. Hitchcock finally settled on Roy Thinnes as Adamson and shot several scenes with him. When Devane became available, Hitchcock fired Thinnes and re-shot all of his scenes. Later, Thinnes confronted Hitchcock in a restaurant and asked the director why he was fired. Hitchcock simply looked at Thinnes until the actor left. Some shots of Thinnes as the character (from behind) remain in the film.