THERE ARE SPOILERS.
I read this 1943 novel in the Kindle edition of Library of America's Women Crime Writers: Eight Suspense Novels of the 1940s & 50s. (Obviously the cover I'm using here is from a previous book publication.) I've seen the film adaptation several times -- and twice more since reading the novel -- and it's one of the classic film noirs.
In a wonderful overview of the collection and analysis of the methods of mystery/crime fiction, film scholar David Bordwell paints Vera Caspary as quite a character: "Vera Caspary was a woman to be reckoned with -- Greenwich Village free-love practitioner, Communist party member, occasional screenwriter, boundlessly energetic purveyor of suspense fiction, passionate paramour of a married man, and advocate for women in prison."
In her appreciation of the novel, Sarah Paretsky says that Caspary had strong feelings about how Laura was presented in the movie: "Caspary fought with director Otto Preminger over the way he depicted Laura’s sexuality in his 1944 film version. Caspary’s rage, as she herself called it, remained so intense that decades after the film’s release, she attacked Preminger (verbally) when she found herself seated near him at a restaurant."
I actually didn't get any sense of a strong sexuality in Laura from my own reading, but I'm willing to admit that I may have just been obtuse. I didn't get any sense that she'd had sex with her boyfriend, Shelby Carpenter, or any of her previous boyfriends, nor did I get any sense that she wanted to have sex with the detective, Mark McPherson, with whom she ends up falling in love. The only depiction of what might be considered sexual feelings on her part that I can remember is when Waldo Lydecker accuses her of a weakness for men with lithe, hard bodies.
The one major difference from the film that I picked up on is that the novel is told from four points of view: It opens (like the movie) with a section from Waldo's point of view as he tells McPherson about the history of his friendship with Laura, then (like the movie) it switches to a section from McPherson's point of view as he prowls around Laura's apartment and begins to develop feelings for her. (To my mind, this is the most sensual part of the novel, as McPherson sniffs her perfume and strokes the fabric of her clothes, almost as if he's trying to become her.) The third section is a transcript of an interview with Shelby Carpenter, which is also depicted in the film, but without the immersive flashback that characterizes Lydecker's narration. Then we get a section from Laura's point of view, and this is more or less completely missing from the film. I wonder if that's what enraged Caspary, because it turns Laura into someone without her own perspective on things; someone whom we only see through the eyes of the men who desire her. Finally the novel switches back to McPherson's point of view, which he shares with Lydecker by quoting some of his thoughts about Laura. Again, this is mimicked in the movie by giving Lydecker the last words spoken.
The film seems like a relatively faithful adaptation of the novel, other than the elision of Laura's point of view. What it helped me to see is how carefully Caspary melded the conventions of the mystery novel and the romance novel. What I'd especially forgotten is that once we learn that Laura isn't the person who was murdered at the beginning of the book, she becomes one of the prime suspects for killing Diane Redfern, who is the person who was mistaken for Laura after her face was blown off by a shotgun while she was staying in Laura's apartment and wearing Laura's clothes. (One change in the movie is that forensics establishes the true identify of the corpse, but only after the detective has already figured out who it was.) The detective is thus not only trying to determine who the killer is, but whether Laura is someone he can trust with his love. It's also a story about a woman trying to pick her ideal kind of man, and it seems very traditional in the way it depicts her choices. Lydecker is a control freak, Shelby is a fop, and McPherson is a manly man. As Paretsky points out, self-control seems to be the redeeming quality. Another major difference between film and book is that in the book Lydecker is a grotesquely fat man who enjoys food and drink too much. He represents an effete parasite class of snobs trying to turn the commoner, Laura, into an artificial treasure removed from her roots, whereas the working class detective can recognize her true value. While the romance aspect of the novel gives it a vastly different feeling from the hardboiled tradition, it's still the hardboiled dick who gets the girl in the end. However, Laura is an agent of her own fate, and the key conflict is the psychological battle between her and Lydecker, which she ultimately wins all on her very own.