In 1939 Los Angeles, renowned private detective Philip Marlowe is approached by the elegant heiress Clare Cavendish to locate her mysterious missing lover, Nico Peterson, a prop master associated with the Pacific Film Studios. Marlowe’s investigation takes a dark twist when he quickly discovers that Peterson is deceased—his life brutally cut short after a night of heavy drinking that resulted in an accident outside of the exclusive and opulent Corbata Club, where his head was tragically crushed by a passing vehicle.
Upon informing Clare of Nico's untimely demise, Marlowe has a chance encounter with Philip O'Reilly, who is the owner of Pacific Studios and is on the verge of becoming England's Ambassador. O'Reilly also happens to manage Clare's mother, actress Dorothy Quincannon. Interestingly, Clare is married to Richard, and she tells him that Marlowe is simply assisting her in finding a missing piece of jewelry. However, as Marlowe digs deeper into the case, he learns from a nearby homeless man that suspicious individuals from Mexico had been frequently visiting Nico's home before his death.
In a surprising revelation, Clare mentions that she has spotted Nico alive and well, driving past her in Tijuana, Mexico. Her claims are bewildering, particularly when she reveals that Nico was an avid collector and stored his treasures in an aquarium. Frustrated by her reluctance to share essential details, Marlowe prepares to exit but unexpectedly runs into Clare's mother, Dorothy, who is oblivious to Marlowe’s actual purpose.
Marlowe also pays his respects at Peterson's grave, where he encounters a mysterious woman who flees before he can speak with her. He persists in his quest for truth, urging his friend Det. Joe Green to launch a murder investigation, given that the body identified as Peterson's may not actually belong to him. In response, Green cautions Marlowe about his relentless pursuit of the truth and mentions that the body was recognized by Floyd Hanson, the owner of the Corbata Club.
Their meeting at the club proves fruitless, as neither can extract useful information from the other. Nonetheless, tensions rise when Marlowe boldly asserts the possibility that Nico may still be alive. Later, he spots the woman from the cemetery—Lynn, Nico's sister, portrayed by Daniela Melchior—and they make plans to secretly meet later that evening at the Cabana Club. However, their rendezvous is interrupted when Marlowe is ambushed by henchmen, whom he skillfully subdues.
Dorothy later approaches Marlowe with her own intentions to find Nico, revealing her complex history with Clare, marking the tumultuous relationship stemming from her years of hiding Clare's existence to protect her movie career. Furthermore, it comes to light that Nico was also serving as a talent agent for actress Amanda Toxteth, who provides insight into his womanizing ways and ties to drug trafficking from Tijuana.
With leads dwindling, Marlowe breaks into Nico’s residence where he encounters Lynn again, but they are quickly attacked by two men searching for someone named Serena. Marlowe is knocked unconscious, while Lynn is taken away. Upon regaining consciousness, Marlowe finds himself in the clutches of drug lord Lou Hendricks and his enforcer, Cedric. Hendricks reveals that Nico had betrayed him by stealing a significant amount of cocaine, and the Corbata Club orchestrated the façade of his death.
Marlowe promptly seeks assistance from his officer friend Bernie Ohls to locate Lynn, while Clare attempts to seduce Marlowe, who manages to resist her advances yet shares a brief dance. Following Clare’s shadowy secret meeting with O'Reilly, Marlowe’s desperation leads him to confront the death of Lynn when Ohls reveals the grim truth of her fate—she was tortured and killed.
With renewed determination, Marlowe infiltrates the club, confronting Hanson, who offers him a drink. Marlowe's instincts tell him that it could be poisoned, prompting him to discard it while feigning fatality. Convinced Marlowe is dead, Hanson’s cronies transport him to a hidden chamber where torturous secrets are unveiled. Under duress, Hendricks admits that the eponymous Serena is actually the mermaid statue enshrined in the aquarium, hiding the missing cocaine.
In a fierce showdown, Marlowe teams up with Cedric to eliminate Hanson and his cohorts, inadvertently demolishing the statue along with the drugs in the process. With the stage set for further confrontation, Marlowe returns home only to discover that the real Peterson awaits him. The actual Nico expresses no remorse for Lynn’s death, indicating a deeper moral complexity surrounding their relationship.
Nico discloses his collection of evidence against O'Reilly, providing Clare with the impetus to protect the studio’s reputation, while Dorothy desires to leverage this information to expose O'Reilly. Yet, in a shocking turn of events, Clare betrays Peterson, shooting him and igniting the prop house to cover her tracks and secure her power within the studio. With Marlowe arriving at the scene, he witnesses the destruction of not just the evidence but the lives intertwined within this haunting narrative, leading Dorothy to offer Marlowe a position as head of security, which he politely declines, instead suggesting Cedric for the role.
