One of the greatest thrills of watching Mulholland Drive (2001) is attempting to infer what David Lynch’s twisted, trancelike narrative tells you without saying anything directly. The first few times it’s viewed, the film seems a complete mindscrew. But after a few more encounters its mysterious components begin to clear up. Subtle clues that previously went unnoticed start to mean something, and more of Lynch’s ten clues to unlocking the film begin to reveal themselves.

Nowhere within Mulholland Drive does anyone directly state that Diane Selwyn (Naomi Watts) is a call girl. There’s nothing outward about that accusation, and it’s likely that millions of viewers have watched the film without ever thinking along those lines. Yet Lynch peppered several things within the story that imply Diane’s “side-job” from acting was that of a high-class prostitute; a lifestyle that coupled and furthered the depression and envy that led her to ordering the murder of her lover Camilla (Laura Elena Harring).

Diane comes from a place of troubled self-worth, which may have originated with her grandparents. The elderly couple that haunts Diane from the film’s beginning to end are always associated with the Jitterbug contest she won years earlier, indicating she likely lived with the couple at that time. It also infers the grandparents weren’t nice to her, so she fled to LA where she could start life as a Hollywood star, giving her the opportunity to life the life of other characters. Her red-headed aunt Ruth (Maya Bond) believed in her, leaving Diane money and a residence when she passed.

Of course, she isn't an immediate star. Aunt Ruth’s money wears out, and Diane moves into a junky hotel downtown (a series of events her dream-like state attributes to Adam Kesher (Justin Theroux) instead of herself.) She also works at Winkie’s diner as a waitress. Struggling, she joins a call girl operation that eventually allows her to live in a nicer home.

Eventually one of her aunt’s friends, Wally Brown (James Karen) allows her to audition for The Sylvia North Story, a film about a woman who was seuxally abused as a child. Since Diane had a poor childhood, she does great in the audition. Camilla is also involved in the film and the two become lovers, eventually moving in together. Diane grows increasingly fixated on Camilla, whose stardom is rising after The Sylvia North Story while Diane’s returns to stagnation. Eventually the two have a falling out and Camilla moves out, more than capable of financing her own residence. Struggling to cope with the emotional attachments in the lonely apartment, Diane switches apartments with a neighbor.

On the night of the drive up Mulholland, Camilla arranges for the limo to stop so she and Diane can walk the rest of the way through the woods. At the party at Kesher’s house, several Hollywood men stare at Diane, implying she may have formerly served them as a call girl. After Camilla and Adam announce their engagement, Diane snaps. The next day she meets a hitman at Winkie’s and orders the hit to end Camilla's life. The hitman tells her a blue key will be waiting for her when the job is done. Diane surveys the diner and sees several things that manifest during her dream - a blue key, the male diner patron, the name Betty. All of these things work their way into Diane's dream in different forms.

She eventually discovers the blue key on her coffee table and enters a severe depression, ultimately killing herself.

Telephones play a conspicuous role throughout the film. We see one ring early on, which nobody answers, and later find that phone in Diane’s apartment. Hollywood guys are seen using phones with ambiguous purpose; a two-fold literal and metaphorical representation of the call girl business. The phone is positioned with a red lampshade (one of Lynch’s clues to unlocking the film), and Diane has red bed sheets. Red becomes a color symbol for the business Diane is wrapped up in, an allusion to the Red Light District famous for this type of activity.

Alan Shaw also notes in his essays that pink and red are prominent contrasts for the Betty/Diane characters. Betty dresses in pink, a more innocent and harmless shade of red. As the innocent and optimistic version of herself, Diane seeing Betty in pink makes sense. He explains that in another scene, “We see three people walking away from the general direction of the sign, one of whom is clearly a prostitute who looks like a doppelganger of Diane, especially because of the color and style of her hair. And what is right behind her as she walks away from the Pink's establishment? It is a long red pole or rod that is being carried by a man that has been conspicuously placed into the scene. The way the rod hangs down and the way it is pointing to her behind make it another clear phallic symbol, indicating that some man has engaged in some sexual activity with Diane that has led her away from her pink persona and into prostitution. This is a color narrative that describes an initial state of pink that is then left behind during a movement toward a red state that involves prostitution. There is even another red lampshade in this scene in the store window the prostitute is walking by while coming around the corner.” The prostitute is also smoking, and we can infer based on evidence in the film's final scenes is an activity Diane took up during her time as a call girl. 

The interpretation of symbols and examination of subtext implies that Diane may have worked as a prostitute. During the dream part of the film, her various encounters with Hollywood executives detached from their real origins and were attributed to various faces and names, as if to shield her own memory from the things she did.