The story's setting was changed from 1940s Los Angeles to 1970s London. The film contained material more explicit than what could only be hinted at in the 1946 version, such as homosexuality, pornography and nudity. Mitchum was 60 at the time of filming, far older than Chandler's 33-year-old Marlowe (or the 1946 film's 38-year-old Marlowe played by a 46-year-old Bogart).
In 1970s England, private detective Philip Marlowe (Robert Mitchum) is asked to the stately home of General Sternwood (James Stewart), who hires Marlowe to learn who is blackmailing him. While at the mansion, he meets the General's spoiled and inquisitive daughter Charlotte (Sarah Miles) and wild younger daughter Camilla (Candy Clark).
Marlowe's investigation of the homosexual pornographer Arthur Geiger (John Justin) leads him to Geiger's employee, Agnes Lozelle (Joan Collins), and to a man she has taken up with, Joe Brody (Edward Fox). He also discovers Camilla at the scene of Geiger's murder, where she has posed for nude photographs, and takes her home safely to a grateful Charlotte.
Returning to the crime scene, Marlowe is interrupted by gambler Eddie Mars (Oliver Reed), who owns the house where Geiger's body was found. Mars's wife Mona hasn't been seen in a while and may have run off with Charlotte's missing husband, Rusty Regan (David Savile). And due to Charlotte Regan's gambling debts, Mars appears to have a hold over Charlotte as well.
Camilla tries to get her pictures back from Brody, who now is in possession of them. Marlowe intervenes but Brody is shot and killed by someone unseen.
A man named Harry Jones (Colin Blakely) comes to Marlowe with a proposition. He is working with Agnes now and she is willing to sell information as to Mrs. Mars' whereabouts. But on the night Marlowe shows up for their meeting, Harry is poisoned by Lash Canino (Richard Boone), a hit man who is working for Eddie Mars.
Marlowe pays Agnes for the address. He tracks down Canino at a remote garage, where he is overpowered and taken prisoner. Mars' supposedly missing wife Mona (Diana Quick) is there as well. At a moment when Canino is out, Marlowe persuades her to set him free. In a shootout, he then kills Canino.
Camilla Sternwood appears to be grateful to Marlowe, and asks Marlowe to teach her to use a gun so she can protect herself. Later, he takes her out to a wooded area so she can learn. He gives her a gun and then goes about setting up some things on a log for her to use as targets. While he is doing this, she points the gun at him and begins pulling the trigger repeatedly—Marlowe was prepared for this and had given her a weapon loaded with blanks. She becomes hysterical at the ruse and he takes her home. It turns out that the emotionally disturbed Camilla had murdered her sister's husband Rusty and that Charlotte had covered everything up with Eddie Mars' help.
After confronting Charlotte with the facts, Marlowe tells her to have Camilla hospitalized. He then drives away from the Sternwood residence the same way he came in, hoping that the gravely ill General will never know the truth about his two wicked daughters.Robert Mitchum as Philip MarloweSarah Miles as Charlotte Sternwood ReganRichard Boone as Lash CaninoCandy Clark as Camilla SternwoodJoan Collins as Agnes LozelleEdward Fox as Joe BrodyJohn Mills as Inspector Jim CarsonJames Stewart as General SternwoodOliver Reed as Eddie MarsHarry Andrews as NorrisColin Blakely as Harry JonesRichard Todd as Commander BarkerDiana Quick as Mona GrantJames Donald as Inspector GregoryJohn Justin as Arthur Geiger
Mitchum had also portrayed Philip Marlowe three years earlier in Farewell, My Lovely, although that film was shot as a period piece rather than set in the present day. Mitchum remains the only actor to play the character in more than one movie, although he is not the only actor to play Marlowe more than once, Dick Powell having portrayed him in an episode of Climax! adapting The Long Goodbye as well as in several radio plays, and Powers Boothe in a series of 1986 dramas made for HBO.
Actors who had earlier played Marlowe in feature-length films include Powell (1944), Humphrey Bogart (1946), Robert Montgomery (1947), George Montgomery (1947), James Garner (1969) and Elliott Gould (1973). Marlowe would be played by James Caan in the 1998 television film Poodle Springs.
Mitchum, Sarah Miles and John Mills reunited for this film, having starred together eight years before in Ryan's Daughter.
Diana Quick performs the song "Won't Somebody Dance with Me", a ballad composed by Lynsey De Paul.
The film opened to mostly mixed to negative reviews – many felt that the film was inferior to the 1946 version, and wondered why the setting was inexplicably changed from Los Angeles to London, England, or why General Sternwood had one British daughter and one who was American. While some critics thought the film better captured the dark touches of Chandler's novel, they felt director Michael Winner didn't give the film the edge that Dick Richards had given Farewell, My Lovely three years earlier.
The Big Sleep has been released twice on DVD:Artisan Home Video (now Lionsgate) under license from Carlton Media (successor in interest to ITC Entertainment) on April 30, 2002 as a Region 1 fullscreen DVD.Shout Factory, under license from ITV Studios (successor in interest to ITC Entertainment and Carlton Media) on September 23, 2014 as a Region 1 widescreen DVD.