Marlowe walks outside and sees Carmen Sternwood. He approaches her and returns her gun. Flirtatious as ever, she asks him to teach her how to shoot. He asks for the gun back until they get to the location where she says they can practice. They drive, following Carmen's instructions. The place is full of empty oil pumps; everything is rusty, old, and desolate.
Marlowe gives Carmen the gun and sets up the cans they are going to use for target practice. As he returns to Carmen, she points the gun at his chest and tells him to stand still. She shoots, but no smoke comes out of the gun. Marlowe stops and grins at her—he had loaded the gun with blanks. As he goes over to Carmen, she begins to shake and then faints. As he is driving her home she wakes up and asks, "What happened?"
Marlowe returns Carmen to her house. He meets with Vivian and tells her what has happened. Marlowe pieces the entire puzzle together in front of her: the blackmail murder, Geiger, Brody, his pictures, Eddie Mars, Canino, and Mona. Vivian claims she is bored with all of it. However, it begins to become "interesting" when Marlowe moves into the Rusty Regan plot.
Marlowe tells Vivian how her sister, Carmen, tried to kill him. He then proceeds to say that Carmen tried to kill him in the same exact way she killed Regan, as Regan had rejected her just as Marlowe has—and Carmen did not like that. Marlowe then says that Vivian paid off Canino to dispose of Regan's body, using the $15,000 that Regan always carried around in his pockets.
Marlowe tells Vivian that Carmen, clearly mentally ill, needs to be taken away to a place where she can be cured. Vivian then confesses, affirming the story Marlowe has just set forth. She tells Marlowe that Regan is lying dead in an oil sump. After Vivian found out her sister had murdered Regan, she decided to get rid of the body because she did not truly love him, and because the police would find out and Carmen would be in trouble. Most important, however, Vivian wanted to keep the murder from her father, the General. It would kill her father to know the truth, and she did not want him to have to think of such things in his dying days.
Marlowe again tells Vivian to take Carmen to get help. He says he will give Vivian three days to go away, at which time he will come out with the whole story. The novel ends with Marlowe reflecting on death—the "big sleep"—and thinking of Silver-wig.
In the final pages of The Big Sleep, we realize that, although Marlowe has solved the puzzle, significant unease remains. Eddie Mars, who stands behind so many murders and crimes during the course of the novel, does not get any just retribution. The secret of the Sternwood family will be kept and Carmen will be cured, not punished. As for Vivian, she will be given the opportunity to escape. Although General Sternwood will die without the painful knowledge of Regan's death, he will also die without knowing the truth.
In light of this untidy conclusion, we may wonder how well Marlowe has done his job. More broadly, we may wonder if a just, happy ending is an impossibility in the world Chandler has created. In the end, the novel's tone and outlook are both positive and negative. We realize that Vivian is not completely evil because she has covered up Regan's murder merely in an attempt to keep a hurtful truth from her father. Just like Marlowe, she is trying to protect the Sternwoods and their name; there seems to be a kernel of kindness behind her dark eyes after all. This is not to say, however, that Vivian—and Carmen—have not committed heinous acts. It is perhaps this reason, this turmoil that arises in the end, that leaves Marlowe thinking there is no way out other than death, the "big sleep."
The last lines of The Big Sleep are about Silver-wig. It is not completely clear why Marlowe thinks of her in the end, and what the significance of his thoughts may be. Marlowe may mean something similar to his thoughts about death—that the world is disillusioning, and that he only desires what he cannot attain. It may, however, be more positive in the sense that the novel ends with Marlowe's thoughts returning to one of the novel's only seemingly noble characters.