Norah (Anne Baxter), a young woman working as a telephone operator, gets a breakup letter from her soldier boyfriend and goes out for a night on the town. After a number of strong drinks, she goes home with a womanizing lech, Harry Prebble (Raymond Burr), and wakes up in his apartment with his dead body. Guilt-ridden hijinks ensue as Casey Mayo (Richard Conte), local reporter, tries to track down the woman responsible for this sensational crime.
The film contains examples of:
- Amicably Divorced: Norah's roommate Crystal is dating her ex-husband Homer. Crystal says Homer is a way better boyfriend than he was a husband.
- As Himself: Nat King Cole appears in a club singing "The Blue Gardenia".
- Asshole Victim: Prebble gets Norah drunk, then takes her back to his apartment and basically tries to rape her. He's hard to feel bad for.
- Chekhov's Gunman: That lady seen in an early scene demanding that Harry call her isn't just establishing he's a cad. She's the murderer.
- "Dear John" Letter: Norah's tailspin starts when she gets a letter from her fiance fighting in Korea, stating that he's fallen in love with an Army nurse.
- "Eureka!" Moment: Mayo has one while sitting in the airport after Norah's arrest, when he hears the song that was playing when the police found the body, which was not the one Norah said she killed him to.
- False Confession: Mayo gets heaps of phone calls from women claiming to be the Blue Gardenia, but none of them have the right information about the case.
- I Have This Friend...: Norah is incredibly obvious about this when she meets with Casey.
- Necro Cam: Harry's murder is shown at the end in typical dramatic flashback style.
- Sympathetic Murderer: It's really more like self-defense, so there's lots of sympathy to be had for Norah. The actual killer is almost as sympathetic—Prebble claimed he would marry her, and then went back on his word.
- There Are No Police: Actually, there are police, but Casey Mayo gets more done with the power of reporting.
- Title Theme Tune: Sung by Nat King Cole, who also appears in the film As Himself.
- What Did I Do Last Night?: Played for Drama with Norah being too blackout drunk to know for sure whether she killed Harry Prebble.
- Worst News Judgment Ever:
- Well, sure, Prebble's murder would be news. But Casey Mayo's "Letter To An Unknown Murderess" column headline probably doesn't deserve to take up the entire front page of the newspaper.
- "CASEY MAYO CAPTURES BLUE GARDENIA" also takes up the entire front page.