Private detective Philip Marlowe is being interrogated by the police. A bright light is blinding him and Marlow appears to be rather dazed if not entirely confused. Lt. Randall’s questions seem implicate Marlow in a string of unsolved murders to which Marlow’s response becomes the flashback that relates the narrative of the film.
Flashback to Marlowe in his office. The evening is late and the visitor is large. Enormous, in fact, as indicated by his name: Moose Malone. Moose wants to engage the services of the private dick to discover the whereabouts of one Velma Valento. Valento is a woman with hair as red as the fires of hell whom Moose has not laid eyes upon for the past eight years. Not that Velma took a powder or anything; Moose is freshly out of stir after serving eight years of a sentence.
Marlowe agrees to follow Moose to the nightclub that used to employ Velma: Florian’s. Once there, however, nobody seems to know who the heck the big lug is talking about. Even the highly intoxicated Jessie enjoys the widespread denial of the very existence of Velma Valento…until Marlowe discovers a picture of the allegedly unknown woman hidden in a file cabinet. Jessie admits to knowing Velma, but insists the woman is dead. Upon discovering that Moose is out of jail, Jessie suddenly goes into hysterics. Marlowe makes his exit from Jessie’s place, but furtively spies on her through a window. In an instant, Jessie is no longer even slightly tipsy, much less drunk as a skunk and is on the horn making a phone call of the utmost urgency.
When he returns to his office, Marlowe is met by the effeminate Lindsay Marriott who hires Marlowe for the mysterious task of waiting to deliver the ransom for pinched jewels. The canyon is secluded and the night is dark and soon enough Marlowe is knocked into a state of unconsciousness. When he finally comes to, he spots a young woman rising over him. She runs away and Marlow discovers Lindsay’s dead body in the backseat.
Back in the interrogation room, Lt. Randall can only shake his head in disbelief at this story of how Marlowe wound up with a corpse in a car. As he releases the detective, the police officer throws a warning toward Marlowe: stay the heck away from Jules Amthor, psychiatrist. Taking this advice on merit-for the timing being—Marlowe heads back to his office and is greeted by a woman saying she is a reporter sent to question him about a jade necklace which has been stolen. Marlowe immediately recognizes this as a ploy and learns that the woman is really Ann Grayle whose stepmother Helen owns the jewelry in question. A quick trip to the Grayle estate introduces Marlowe to a very old Mr. Grayle and a very young and hot Helen who explains the value of the missing necklace. It is worth $100,000. What’s more, the necklace was taken from her by a thug with a gun. Helen also confesses that the late Mr. Marriott was her friend and she charged him with the responsibility of delivering the ransom for the stolen jade. Finally, Marlow also learns that Marriott was a patient of Amthor.
No sooner is this information learned, than Amthor shows up at the Grayle estate. Marlowe warns Amthor that the police are investigating him, but then makes a quick exit. Later, Marlowe gets a visit from Helen Grayle and invitation for drinks at the Coconut Beach Club where he spots Ann. Ann makes an offer to hire Marlowe, but when Marlowe excuses himself to speak with Moose who has also shown up, she has disappeared when he returns. Fortunately, she’s left behind both her phone number and address.
Marlowe brings Moose to Amthor’s apartment and accuses the quack of being a key player in an intricate web of blackmail scams with his partner Lindsay Marriott. Upon learning that Marlowe does not have possession of the necklace, Amthor knocks him out cold.
Marlowe finally, barely, comes back into the conscious world three days later. He has been locked inside a room and fed a continual diet of drugs to keep him firmly entrenched within the twilight world between waking and sleeping. He manages to escape the room and stumbles his way to the office of Dr. Sonderborg. Only after grabbing the doctor’s gun does Marlowe manage to break free of the premises entirely. Out on the street, who should appear but Moose who gets Marlowe safely inside a cab. When Marlowe informs Moose that Velma and Amthor are somehow involved, Moose takes off alone.
A less woozy Marlowe shows up at Ann’s apartment, ready to admit that he recognizes her as the woman standing over him when he came to back in the canyon. Ann also makes the confession that she discovered Marlowe’s address on Marriott’s dead body. Just then, Lt. Randall arrives and Marlowe informs him about Dr. Sonderborg and the necklace. Ann and Marlowe drive together back to the Grayle mansion and come upon a distressed Mr. Grayle. The distress results from his just having learned that Lindsay Marriott had been renting the old man’s beach house. This news fills him with suspicion that his young wife and Marriott had been fooling around and more.
Marlowe and Ann decide to take a drive to the beach house. When Marlowe takes her into an embrace and kisses, Ann responds by suggesting that he is using romance merely as a means of pumping her for information. As they begin to argue over this matter, Helen interrupts them and Ann turns her anger toward her stepmother with accusations of golddiggery. She angrily exits the house on the beach, leaving Marlow and Helen behind. Helen decides to win Marlowe’s sympathy over to her side with the information that Amthor had become aware of her promiscuously adulterous nature while she was a patient of his and had used it to blackmail her into handing over the expensive necklace. She then makes the suggestion that Amthor killed Marriott after learning of his plans to double-cross him by taking the necklace for himself. Helen kisses Marlowe and then begs him to help her get rid of the insidious Amthor. Marlowe agrees and the plan is laid for him to entice Amthor out to the beach house the next night by promising he will have the necklace with him.
Marlowe heads straight for Amthor’s apartment only to discover that his neck has been broken; apparently by a very powerful person. Marlowe is studying an autographed photo of Velma situated on Amthor’s desk when Moose enters the room. Moose insists that the woman in the picture is not Velma at all. Marlow promises Moose that he and Velma will be reunited and the next night Moose heads to the beach house with Marlowe. While Moose waits outside, Marlowe cautions Helen that Amthor is not far behind him. She reveals the necklace with the story that the entire story of being robbed at gunpoint was a fake. Marlowe responds to this confession by calling her Velma and making the accusation that she is the killer of Lindsay Marriott. Marlowe furthers postulates that Jessie Florian’s phone call he witnessed was to Helen to warn her that Moose was out of jail and hot on her trail. Marlowe also proposes that if Ann hadn’t shown up that night in the canyon he himself would have joined Marriott among the dead.
Helen responds to Marlowe’s connecting the dots by pulling a gun on him. At that point, both Ann and her father interrupt the proceedings. Helen prepares to pull the trigger aimed at Marlowe, but before she can complete the action, Mr. Grayle fires his gun at her. Moose rushes in at the sound of gunshots and discovers that his beloved Velma lies dead. Enraged by this loss, he makes a threatening movement toward Mr. Grayle who is forced to fire Moose in self-defense of his own safety. Just as he does so, however, Marlowe tries to jump between the gun and Moose. The explosion blinds Marlowe to the stone cold reality of what happened. The sound of the shots ring in his ears, but Marlowe cannot see the visual evidence of what happened after Grayle pulled the trigger.
Marlowe is relating this event to Randall back inside the interrogation room and Lt. Randall only releases him from custody when his bizarre and unlikely story is corroborated by Ann. Both the detective and Marlowe learn from Ann that Moose and her father are both dead along with Helen/Velma. Marlowe turns over the jade necklace to the lieutenant and is guided out of the police station while he confesses his true feelings for Ann. Eyes bandaged from the result of the gunshot, Marlowe steps into the cab unaware that Ann is right behind. Only the aroma of her perfume awakens his senses to her presence beside him and the film fades out on their kiss.