A lot of the heart of film noir is in how a person's actions reflect on his or her self-image. 1954's Naked Alibi stars Sterling Hayden as a police chief who goes rogue to catch a killer, blurring the line between lawman and lawbreaker, but the best noir character in this movie is Gloria Grahame.
She doesn't show up until thirty minutes into the movie in a little Mexican border town where she sings a Cole Porter song about how men aren't what they try to make you believe they are.*
She doesn't know how right she is. Her long-time boyfriend Al shows up in town again after one of his extended absences. She doesn't know, but she suspects, the reason he's gone so much is that there's another woman. In fact, he has a wife and kid who we met at the beginning of the film. This is in a town up north where Al's a baker and Chief Joe Conway (Hayden) is trying to bust him for the murder of three cops.
This is why Joe stays on Al's trail even after he's fired for a picture that emerges seemingly showing him beating Al in an interrogation.
The audience doesn't see anything especially crooked about Al at this point (this is before he goes down to the border town) so we have to take it on faith that Joe's right. Since he's played by beefy, angry Sterling Hayden, the crook from The Asphalt Jungle, we can't be sure our faith is justified.
Grahame's character, Marianna, takes Joe in and plays nurse after a few guys mug him.
She finds a newspaper clipping in his pocket that suggests Al might be a killer. Her dilemma over whether or not to help Joe motivates the whole rest of the film. She tells him how she's moved from town to town all her life and we have the impression her trust has been betrayed more than once. What pains her most about this seems to be how it prevents her from being who she wants to be. She doesn't know how to stick by the people she loves because she's never able to tell who's real or who isn't. And she's growing more conscious of the fact that she's running out of time.
*Her singing voice is dubbed by Jo Ann Greer.
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