Marlowe drives Carmen back home, where he meets with Vivian and relates the events that have just transpired.
Marlowe tells Vivian that Carmen had tried to kill him, just like she had killed Regan. Putting together all the pieces of the puzzle, Marlowe explains that Regan had rejected Carmen (just as he'd done), and we all know by now that Carmen can't handle rejection. Marlowe concludes that Vivian had to pay off Canino to dispose of Regan's body, using the $15,000 that Regan always carried around with him.
Vivian finally confesses that Marlowe's right. She reveals that Regan is buried in an oil sump. When Vivian discovered that her sister had killed Regan, she covered up the murder to protect Carmen and, more importantly, to keep Regan's death from her father, who would have been devastated to know the truth.
Marlowe insists that Carmen is mentally ill and needs to be hospitalized. He says that he'll give Vivian three days to get out of town, or else he'll inform officials about the events.
As Marlowe drives off down the hill, he reflects on the nastiness of life and how the only way to escape life is through death, what he calls the "big sleep." He thinks of Silver-Wig, who he never sees again.