The film follows a day in the life of two sisters, Olga (Aline MacMahon) and Myra (Ann Dvorak). Both work in an auto camp in the middle of the Californian desert. Olga is the older sister who has no problem getting down and dirty with “men’s” work —fixing up cars, being self-reliant, not wearing any dresses—and has seen enough of the world to know that it's not all that it’s cracked up to be. Myra, on the other hand, is young and naïve and dying to be somewhere exciting.
As the desert day gets hotter, two men on the lam from a robbery come in called Gerry (Preston Foster) and Jeff (Lyle Talbott). It turns out Gerry and Olga have a shared past: Olga was a cabaret dancer in Tulsa, and Gerry was her abusive boyfriend. Another trio of characters come in to the picture: wealthy divorcees, Mrs. Tifton (Glenda Farrell) and Mrs. Ashton-Ashley (Ruth Donnelly), and their chauffeur, Frank (Frank McHugh). Throughout the day, Gerry and Olga have some sexual tension while he plans to steal from the wealthy women. Meanwhile, Myra wants to sneak out on a date with a man her sister disapproves of, and the divorcees have some wacky hijinks with their chauffeur. But at the end of the night, both sisters are disappointed with their choice in men.
See The Petrified Forest for a similar setting.
Heat Lightning demonstrate the following tropes:
- All Girls Want Bad Boys: Deconstructed: Myra wants to go to a dance with Steve who ends up abusing her. Olga, on the other hand, refuses Gerry's advances but then falls for him once more only to be used by him. She promptly shoots him dead.
- Belligerent Sexual Tension: There’s heavy doses of it between Olga and Gerry, but it’s never Played for Laughs in any shape or form.
- Big Brother Instinct: Olga has a tendency to scare off any man that comes near Myra, but it turns out both have very bad taste in men, so Olga’s instinct isn’t without foundations.
- Coincidental Broadcast: Gerry just happens to turn on the radio to hear about the police apprehending the wrong man for his crime.
- Doesn't Trust Those Guys: Olga lets a Mexican family stay outside during the night since they can’t pay for one of her shacks. Mrs. Ashton tells Olga that she doesn’t trust the Mexican family and wants her jewels somewhere safe. Ashton is considered nonsensical and bigoted for saying this.
- Foreshadowing: The heat lightning throughout the night foreshadows the traumatic events of the evening.
- Henpecked Husband: The man that first comes to the auto camp is very much pushed around by his wife.
- Hoist by His Own Petard: Gerry seduces Olga to distract her from the jewels, but his plan fails to take into account Olga’s wrath and the fact that she has a gun. And kills him at the drop of a hat.
- Manipulative Bastard: Gerry seduces the reluctant Olga for a chance at stealing some jewels.
- Old Flame: Gerry to Olga. Olga knows he’s bad news and has a hard time shaking the lingering feelings he’s awakened.
- Promotion to Parent: It’s all subtext, but it looks like Olga and Myra were left parentless at a young age. Olga had to pick up the slack and become a mother to Myra and protect her from the dangers of the world.
- She Cleans Up Nicely: Continually annoyed by Gerry’s remarks that she’s no longer the girl that she was before, Olga takes off the mechanic garb and puts on some makeup and a dress for his benefit. They sleep together almost right after.
- Tomboy and Girly Girl: Olga is the traditional tomboy while Myra wears dresses and lipstick and all the other traditionally girly things.
- Trigger-Happy: Gerry didn’t need to kill the clerk in his stick up with Jeff but did it just because he wanted to. And then in the end, Olga just shoots Gerry dead when she finds out he only slept with her to distract her.
- Unkempt Beauty: Olga since she’s usually covered in car grease and sweat.
- Video Credits: As most pre-Code films from Warner Bros, we get a video introduction of our actors.
- Wham Line: “I just killed a rat!”
- Wrench Wench: Olga, for the most part of the film, is dressed up in a mechanic's garb and is working away at any local’s car.
- You All Meet in an Inn: All the principal characters find themselves at Olga's auto camp, and the story follows their day there.
