On a stormy night, in a forest outside of 1940s Los Angeles, California, a car swerves off the road and over a cliff. At a detective agency, private investigator Rigby Reardon reads the newspaper reporting the death of scientist, philanthropist, and cheesemaker Dr. John Hay Forrest. Suddenly, Dr. Forrest's daughter Juliet knocks at the door, but when she notices the headline announcing her father’s death, she faints into Rigby’s arms. Enamored with Juliet’s beauty, Rigby kisses her and lays her on the couch. As Juliet awakens, Rigby guesses that she suspects her father’s death was not an accident. Juliet explains that her father had written a list of names on a torn scrap of a dollar bill, which she believes connected him to a conspiracy. She pays Rigby a $200 advance and gives him the key to her father’s office in the city. At Dr. Forrest’s office, Rigby uncovers two lists titled “Enemies of Carlotta” and “Friends of Carlotta.” On the latter slip of paper, he notices the names “Kitty Collins” and “Swede Anderson.” A man posing as an exterminator enters the office and shoots Rigby in the arm. Rigby pretends to be dead, and the man steals the lists from his pocket. In pain, Rigby goes to Juliet’s house, where she uses her mouth to suck the bullet from his wound. She explains that Kitty was her father’s mistress, and Swede was Kitty’s boyfriend, both of whom live in Santa Barbara. She shows him a paper that reads: “Thanks for the check. In case I’m indisposed, that dollar you gave me for safekeeping is in the top of the sugar bowl. –SHH.” Juliet says “SHH” stands for Samuel H. Hastings, her former drunkard brother-in-law. Juliet phones her hypochondriac sister, Leona Hastings, to ask about Samuel’s whereabouts, but Leona cries hysterically and hangs up. As Rigby leaves to look for Samuel, Juliet tells him to leave messages of any news with her cleaning woman. Upon hearing the words, “cleaning woman,” Rigby becomes enraged and throttles Juliet around the neck. After calming down, Rigby confesses that his father ran off with their family's cleaning woman when he was a child, which caused his mother to die of a broken heart. He later finds Samuel in a hotel and gives him $5 in exchange for the dollar bill in Samuel’s sugar bowl. Dr. Forrest’s torn scrap matches with the bill, which contains a copy of Dr. Forrest’s “Friends of Carlotta” list. Rigby drives to Santa Barbara and finds Kitty Collins working as a lounge singer, but when he mentions Carlotta, Kitty excuses herself from the conversation. The next day, he follows her to a restaurant. When she notices him watching her, she removes her crab-shaped broach and drops it in her soup. Rigby retrieves the broach from the kitchen and discovers that there is an “Enemies of Carlotta” list hidden inside it, with many of the names crossed off. The only remaining name is Swede Anderson, who Rigby finds unconscious in a grimy apartment. While Rigby prepares coffee in the kitchen, two men barge in, kill Swede, and shoot Rigby in the arm. Juliet again removes the bullet and Rigby calls his detective friend, Alan Marlowe, instructing him to come over. Juliet finds a train station locker key in her father’s desk and Rigby deduces the locker number. When Marlowe arrives, Rigby asks him to investigate the names on Kitty Collins’ “Enemies” list. Rigby opens the locker at Los Angeles Union Station, where he finds more copies of the two lists, including the name and address of F. X. Huberman. He boards a train to visit Huberman, and is followed into his compartment by a handsome man. Rigby lulls the man to sleep and sneaks off the train without his pursuer. Upon reaching the house, Rigby realizes that Huberman is actually a woman. Huberman spikes Rigby’s drink with drugs and he passes out. Huberman steals the locker key, and Rigby later wakes up in his office with Juliet standing over him. She announces that Samuel Hastings is dead and that she found a note containing the date and issue of an old New York Times article. The article mentions the South American cruise ship, S.S. Immer Essen, which Samuel boarded after separating from Leona. Marlowe calls Rigby’s office and tells him that Walter Neff, owner of the cruise line, has a weakness for beautiful blonde women. Juliet offers to dye her hair and pose as a spy, but Rigby refuses, attempting to hide his romantic interest in her. After failing to hire various former girl friends and associates as his spy, Rigby seduces a rich society woman named Jimmi Sue Altfeld and convinces her to agree. Following a meeting with Jimmi Sue’s disapproving father, Mr. Altfeld, Rigby is beaten up by a group of men. Juliet finds him and begs him to end the investigation, but he plans to disguise himself as a blonde woman. While wearing women’s clothes and makeup, Rigby seduces Walter Neff, drugs his drink, and steals the passenger list for the S.S. Immer Essen, containing the name of Captain Cody Jarrett. Before Rigby, disguised as the captain’s mother, speaks with Jarrett, Juliet confesses her love for him and they kiss. Believing Jarrett to be in danger, Rigby poses as a prisoner to protect him, and attempts to learn more about Carlotta’s identity. That night, Jarrett breaks out of prison, throws Rigby in the trunk of a car, and shoots him in the arm. When Rigby returns to his office many hours later, he and Juliet begin to make love, but she leaves to get medicine for his bullet wound. He receives a telephone call from a former lover, Margaret Croyden, which Juliet overhears and misinterprets. Her heart broken, she telephones Rigby from a telephone booth and tells him to cancel the investigation. Later, Marlowe reveals that Carlotta is actually a South American island near Peru. Rigby travels to Peru and finds Kitty Collins and Carlos Rodriguez, and an old war friend, who gives him the name of Kitty Collins’ murderous lover, Rice. A few days later, Carlos telephones to inform Rigby that a plane full of Germans gave Rice a suspicious packet of instructions, but Kitty cuts the telephone line. She fixes Rigby a drugged drink and he passes out. When Rigby awakens, Rice attempts to smother him with a pillow. Rigby fires his gun, prompting Rice to flee. Rigby and Carlos chase Rice through the crowded street, but Carlos is shot in the shoulder and falls behind. Rigby kills Rice and steals his top secret papers. He follows the instructions to a warehouse, where Juliet and her father, still alive, speak with their family butler, who is dressed in a Nazi uniform. Although Rigby believes Juliet betrayed him, she insists that she was tricked by the butler, Field Marshall Wilfred VonKluk, and only knew to come to Carlotta after Marlowe informed her. VonKluk reveals that that Dr. Forrest had discovered a powerful, destructive cheese mold and the Nazis tricked him into sharing the information in order to create an explosive that would obliterate the entire U.S. Forrest realized the plan and composed a list of VonKluk’s agents to take to the Federal Bureau of Investigation. As a result, VonKluk faked Forrest’s death and kidnapped him. While testing the cheese mold on the island of Carlotta, passengers of the S.S. Immer Essen witnessed the land mass disappear, forcing VonKluk to label them as “enemies” and assassinate them. VonKluk announces that he has planted a series of cheese bombs throughout the U.S. Juliet tricks VonKluk into say the words “cleaning woman,��� prompting Rigby to lose control and strangle the field marshall. VonKluk flips a switch and detonates the city of Terre Haute, Indiana, but Rigby kills him and stops further destruction. Carlos arrests the remaining Nazis as Rigby and Juliet kiss.