The film starts with a Spooky Séance contacted by Blanche Tyler (Harris). Her latest client is elderly Julia Rainbird (Cathleen Nesbitt), who wants to locate her last living relative: the illegitimate son of her sister, given up for adoption decades ago. Now that boy is supposed to inherit the family fortune, and Julia offers Blanche $10,000 to find her heir. Blanche is actually a Phony Psychic. The facts she reports to her clients are the results of some detective work by her boyfriend, George Lumley (Dern), an unemployed actor and part-time cab driver. The two bumbling detectives now have proper motivation to find that heir.
The scene shift to the heir Arthur Adamson (Devane) and his girlfriend Fran (Black). They are both Wicked Cultured. Arthur murdered his foster parents many years before and now works as a jeweler and upper-class house. He and Fran actually earn most of their money from a highly-successful career as kidnappers, their targets being millionaires and dignitaries. By the time the film starts, the thrill of the work has become part of their motivation. Danger turns them on and really helps their sexual activities. These two are dangerous people.
Naturally, seeking out the two master criminals turns out to be a more dangerous mission than Blanche and George expected.
Alfred Hitchcock's 54th and final film, capping a career that spanned more than 50 years. He died four years later.
This film provides examples of:
- All Women Are Lustful: A horny Blanche wants George to spend the night, but he's too tired.
- Artistic License Religion: The Shoebridges and the Maloneys are apparently supposed to be Mormon, with the stonemason referring to the Shoebridge burial as being done by the "First Church of Latter-day Saints" and a quotation from the Book of Mormon (2 Nephi, chapter 9) read at Joe Maloney's graveside service. But the church-related material in the film seems more reminiscent of Catholicism or Anglicanismnote .
- Aside Glance: Blanche winks at the viewers as the movie ends.
- Creator Cameo: Alfred Hitchcock makes an appearance in silhouette behind the door marked Registrar of Births and Deaths.
- City with No Name: Unlike most Hitchcock films which feature an iconic city or landmark, the location is kept vague except it's obviously in California. San Francisco and Los Angeles were both used for exterior shots, with San Francisco's famous black-on-white street name signs visible at several points.
- Digital Destruction: The Blu-Ray has an uglier transfer than other Hitchcock movies do.
- Double-Meaning Title: Family Plot refers to the Shoebridge family gravesite, Eddie murdering his adoptive parents, and Blanche's scheme to find the Rainbird heir so she can collect her money.
- Even Evil Has Standards: While Fran readily goes along with Arthur's kidnapping schemes, she's reluctant to murder Blanche, as Arthur intends to. She doesn't even want to drug Blanche at first.
- Every Car Is a Pinto: We don't see Joe Maloney's car blow up after he careens off a mountain road, but we do see the satisfying fire afterwards.
- Getting Crap Past the Radar: The dialogue is loaded with Double Entendre.
- Hidden in Plain Sight: Arthur hides the diamonds from his kidnappings (the diamonds are the ransom payment) in the chandelier in the hallway of his house. Blanche is the one who discovers this at the end.
- Hoist by His Own Petard:
- Joe Maloney tries to kill George and Blanche by having them lose control of their car on a steep mountain road. Instead that's how he ends up dying.
- At the climax Arthur and Fran get locked up in the hidden chamber where they kept their kidnapping victims.
- In the Style of...: The John Williams score sounds a lot like Bernard Herrmann at times.
- Internal Reveal: We find out that Arthur Adamson=Eddie Shoebridge long before George and Blanche learn that fact.
- ISO-Standard Urban Groceries: Blanche carries the standard brown paper bag with lettuce sticking out. Used for a bit of comedy when she plops the bag down on the hood of the car and George has to carry it in.
- Make It Look Like an Accident: Arthur plans to kill Blanche and stage the scene to look like a suicide.
- Maybe Magic, Maybe Mundane: The final scene leaves it ambiguous whether Blanche might actually have psychic powers.
- Never Found the Body: Turns out there's nobody in Edward Shoebridge's grave, as the police never found his body after the house fire. That's because Eddie assumed the identity of Arthur Adamson.
- Outlaw Couple: Two different couples—The "good" couple is a Phony Psychic and her boyfriend who assumes different identities to gather intelligence to help her in her cons. The evil couple practices kidnapping for ransom and jewel heists.
- Phony Psychic: Blanche Tyler, complete with Large Ham voices supposedly channeling dead spirits. Possibly subverted in the very last scene.
- Porn Stache: Arthur's unappealing mustache establishes him as slimy and venal.
- Precision F-Strike: Some swearing (mainly from George), which is a bit jarring for a Hitchcock film (Family Plot is PG but there's actually more swearing here than in the R-rated Frenzy).
- Samus Is a Girl: When the mysterious black-clad woman goes into the police station with a ransom payment, the cops are surprised to find that she's a woman. ("You called yourself 'The Trader', so we thought you were a man.")
- Self-Made Orphan: Arthur/Eddie murdered both his adoptive parents in a house fire.
- Shout-Out: Blanche lives at the corner of Castle Heights and Bates. While "Castle Heights" was a fake sign (the scene was actually filmed on Lexington Avenue in the Silver Lake section of Los Angeles), the adjoining street really was called Bates Avenue. Hitchcock and his crew obviously recognized the connection to Psycho and left the sign untouched.
- Slobs vs. Snobs: Blanche/George are the Slobs (low-level con artists), Fran/Arthur are the Snobs (high-class jewel thieves).
- Smug Snake: Arthur clearly has a high opinion of himself and his criminal exploits, and is constantly grinning.
- Spoiler Cover: The tagline on the poster in the original release flat-out gives away a crucial part of the main plot twist: "There's no body in the family plot".
- Spiritual Successor: The screenplay was by North by Northwest's Ernest Lehman, and the theme of average people who unwittingly get wrapped up in a Wicked Cultured villain's schemes is common to both films. Also, George and Blanche's car danger recalls both the drunk driving scene and the crop duster scene from the earlier film.
- Too Dumb to Live: Joe Maloney's decision to turn around and try to run over Blanche and George after the Vehicular Sabotage fails ends up costing him his own life.
- Unexpected Inheritance: Subverted. Arthur turns out to be the sole heir to a vast fortune—which he never gets, as he's going to prison.
- Vehicular Sabotage: The brakes on George's car are tampered with, sending he and Blanche hysterically careening down a winding mountain road.
- Villain with Good Publicity: Arthur Adamson is a respected jeweler, but behind the scenes he's a successful kidnapper and jewel thief.