The Girl Who Knew Too Much is often mentioned as the beginning of the giallo genre. That goes a little too far: There are giallo elements here, but this is not as fully formed an example of the genre as is Blood and Black Lace. This is, as the title suggests, a mystery/thriller with a strong Alfred Hitchcock influence. The debt is obvious, but it has its own approach and never feels derivative.
The film begins on a flight from New York to Italy. Nora Davis (Leticia Román), traveling to Rome to visit her ailing Aunt Ethel, accepts a cigarette from a stranger. The chivalrous gent gives her the whole pack, but when he is arrested at the airport with a suitcase full of cocaine, the cigarettes are revealed to be marijuana.
I see you laughing. She smoked the cigarette- on board an airplane, no less- and nobody noticed that it smelled funny? Welcome to 1963: Nora is at least once referred to as "naive," and the movie as a whole has an innocent charm. That ingenuousness would be gone from Mario Bava's work by Blood and Black Lace the next year, but here the darkness is contrasted with a cute sweetness. It's similar to a playfulness that sometimes peeks through Hitchock's work, but it's far more blatant.
Nora arrives to find her aunt attended by her physician, the young and friendly Dr. Marcello Bassi (John Saxon). Ethel takes a turn for the worse that night. The phone is out of service, so Nora runs to get help but is mugged in the plaza outside. Knocked cold, she comes to and has a hazy vision of a woman's murder. She slips back into unconsciousness, and someone douses her with booze. The police take her for a drunk, and she wakes up in a hospital.
A detective interviews her but doesn't believe her story, as there is no evidence that a murder has occurred. Doctors believe her delusional, but Bassi comes to her rescue. He falls short of believing her, but he gets her released from the hospital and takes her to see the city.
These movies often feature a suspicious inspector as a plot device, but usually more in the sense of disbelieving the suspect's story. There's usually no doubt that a crime has actually been committed. The fact that she was drugged adds an unreliable narrator element to the story: Is it possible that the whole thing was imagined? Visual and auditory distortions accompany her viewing of the murder. It is implied that these are the result of her getting conked on the head, but there is a possibility that something else was the cause. Her half-baked idea of stringing up a trap in the house looks like a stoner enterprise, and there's at least one sudden jump in scene that suggests a fantasized event.
A neighbor, Laura Craven-Torrani (Valentina Cortese), befriends Nora. Laura has a large house that overlooks the plaza where the incident occurred. She is leaving for Switzerland, and she insists that Nora house-sit for her.
Laura turns out to have a mysterious back story. Her sister, Emily Craven, was stabbed to death ten years earlier in the same plaza, in full view of Laura's home. Emily was the third and final victim of a serial killer whose crimes were called the "Alphabet murders" because they occurred in alphabetical order.
So, if you're following, there was a murder of a woman whose name began with "A," then a "B," and Emily Craven was "C." What's next? "D," as in..."Davis?" It's obvious where this is going. Nora is on a personal mission to prove that what she saw was real, and she also has to avoid becoming Alpho's next victim.
The discovery of the "Alphabet murders" connection raises an intriguing possibility: Was the murder witnessed by Nora actually Emily Craven's murder, seen through time as though it were happening today? This psychic element introduces a hint of the supernatural. Such supernatural elements are rather common in gialli, which may be part of the reason they fit so well into the horror genre.
The gender of this story is reversed with respect to most later gialli. Even in the Hitchcock films by which this is inspired, the protagonists are typically male. Female giallo protagonists tend to serve as the killer's (and the audience's) focus of attention while a male character carries out the actual investigation. It would be interesting enough if that were a break from expectations, but if the genre originated here, there were no expectations. Funny how all the imitators switched the character's gender, as though crime investigation were an unsuitable activity for a woman. Maybe Italian audiences were resistant to seeing a woman in a traditionally masculine role, and in this case casting the character as an American made it less objectionable.
Shadows and darkness are used as effectively as in Black Sunday. Gothic horror elements exist, but they smoothly blend with mainstream mystery elements and touches of lighthearted humor. There's even a streak of romance in Nora's relationship with Bassi, a theme similar to the one played out in Deep Red.
The Girl Who Knew Too Much combines mystery and horror elements in a way similar to what would soon become known as a giallo, but it's not a fully mature example of the form. As much credit as this gets for influencing the genre, it's odd that nobody has pointed out that it is an early example of another exploitation film genre. The use of marijuana cigarettes as a plot device makes this a stoner film. Veg on that, man.