Alfred Hitchcock's final, very 1970s film entangles two plots. A charlatan medium, Blanche Tyler (Barbara Harris), and her actor-cum-cabbie boyfriend, George Lumley (Bruce Dern), uncover a real gem of a secret while trying to part wealthy old Julia Rainbird (Cathleen Nesbitt) from a bit of her money. Her deceased sister gave up an illegitimate baby years ago. Rainbird wants to find him, since he's her only remaining relative. They take on the legitimate case, because she's willing to pay good money, and the pair have developed considerable detective skills.
Meanwhile, a charming but sinister gem dealer, Arthur Adamson (William Devane) and his partner, Fran (Karen Black), run some side businesses: kidnapping for ransom and illegal jewel trading. They have a creepy cell in their basement, where they temporarily hold their victims.
All of this comes together in a plot involving murder, an empty grave, and a good deal of black humor. Our psychic scam artists-turned-detectives, at turns clever and clueless, find themselves up against real criminals. A murder attempt leads to a harrowing, out-of-control ride down a mountainside road, recalling Hitchcock's North by Northwest. The film also contains references to Psycho.
A few elements feel displaced. The small village whence hails thug-for-hire Joseph Maloney (Ed Lauter) has an American-style roadside cafe, but it feels curiously British, as does a plot to kidnap a prominent bishop. The specific occult trappings would be more at home in the early 70s, the decade's ongoing obsession with the paranormal notwithstanding. These elements likely reflect the movie's source. Ernest Lehman adapted the script from Victor Canning's 1972 novel, The Rainbird Pattern, which takes place in England.
Family Plot features a soundtrack by John Williams, then solidifying his position as Hollywood's favorite composer. It took criticism for being lesser Hitchcock, but, honestly, that's good enough.