English: Knife of Ice) is a 1972 giallo film directed by Umberto Lenzi and starring Carroll Baker, Evelyn Stewart, and George Rigaud.

"[6] A famous singer, Jenny Ascot, visits her artist cousin Martha Caldwell at her home in the town of Martinet, located in the Spanish Pyrenees.

Martha sees the strange man stalking her at the cemetery during Jenny's funeral, and when fleeing, he drops his pendant of a goat, revealing him as a Satanist.

Moments later, police phone the house, and Dr. Laurent answers: They inform him that Annie's corpse has been discovered in the woods, her throat slashed.

During a rainstorm, police catch the man, British hippie Woody Mason, breaking into a local doctor's office and stealing morphine, but are unable to stop him when he flees.

Police subsequently find Woody in a nearby cemetery and apprehend him, but he denies any involvement in Annie's murder, nor that of the teenage girl, whom he was dating.

Christina's murder prompts police to reopen their investigation, and Woody is ultimately acquitted of his charges when an autopsy proves that his girlfriend, the girl in a ditch, died of a heroin overdose.

As Martha is escorted away, she regains her speech for the first time since childhood, and begins reciting the Lewis Carroll poem "The Mouse's Tale", which she once performed for her schoolmates as a child and listened to in tapes throughout the film.

[8] Lenzi initially considered directing Baker in a remake of the 1946 American horror film The Spiral Staircase—which also follows a mute woman stalked by a killer in a rural country house—but instead chose to write an original screenplay utilizing a similar plot device, but subverting it with a twist ending in which the villain is revealed to be the main character all along.

[8][9] Thematically, Lenzi stated: "It was a movie in which I attempted to blend all the elements of psychological distortion of my previous films with a little bit of horror.

"[9] The character of Woody Mason, a deranged hippie Satanist who serves as a red herring in the plot, was loosely based on Charles Manson.

[8] Lenzi co-wrote the screenplay for Il coltello di ghiaccio with Antonio Troiso, a young screenwriter who died of cancer at age 30, shortly before the shooting of the film began.

Il coltello di ghiaccio features frequent use of close-up shots of characters' eyes, which has also been noted as a "Fulci trademark".

[6] With Baker secured for the lead role of Martha Caldwell, Lenzi cast fellow American actor Alan Scott—who had worked primarily in bit parts in European films—as Dr.