Unlike Kuei's later horror-gorn films which are set in contemporary times, this one is set in the past — specifically Shanghai in the 1930s, where a once-wealthy family, the Chans, have fallen on hard times. With most of their family members leaving the country or dying of diseases, what's left of the clan's treasure is under possession of Lady Chan Sau-Ying, the only daughter who is stricken with tuberculosis.
The son-in-law, Yeung Chun-yu, married himself into the Chans for their wealth, but with the family dying off left and right and denied of the inheritance which is sealed in the Chan family's vault, Chun-yu is determined to make his wife, Lady Chan, suffer and remain as miserable as she could until her death. But the arrival of Lady Chan's close friend, Leung Yi-Wah from the rural countryside to find a job, might turn the long-suffering wife's fate around... but NOT for the better.
Kuei Chi-hung would direct two sequels, Hex After Hex and Hex vs. Witchcraft, but the follow-ups are actually screwball horror-comedies which are mostly In Name Only.
Hex contains examples of:
- Always Identical Twins: It turns out Lady Chan Sau-Ying have a secret identical twin sister, Chan Sau-Fong, which she never mentioned for the entirety of the film. In fact, the hauntings and supernatural phenomenon throughout the movie, turns out to be the twin inflicting the worse psychological torment possible on the perpetrators responsible for Sau-Ying's death.
- Asshole Victim:
- Chun-yu ends up suffering excessive psychological trauma from believing his wife had returned from the dead to haunt him, to the point where he ends up throwing himself to his death. Nobody cares.
- Leung Yi-Wah gets tormented to the point where she lose her sanity. But being a False Friend and backstabbing Manipulative Bitch, she gets no sympathies.
- Bald Woman: Leung Yi-Wah at the end of the film; in order to exorcise Lady Chans restless soul, she had to shave every inch of hair on her body, and allow a priestess to paint Buddhist inscriptions all over her naked body. It doesnt work, because there NEVER was a haunting from a Vengeful Ghost in the first place? Also provides a Cover Drop.
- Blood from the Mouth: Lady Chan Sau-Ying at the moment of her death. Seeing her supposedly dead husband by her bedside, her tuberculosis already ravaging her body to the point of being near-fatal, and NOT helped by the numerous amounts of hallucinogens she had consumed through spiked medicine... Lady Chan ends up falling off her bed, head-first, breaking her skull and puking blood all over the bedroom floor.
- Desecrating the Dead: Chun-yu, after waking up and finding his wifes decomposing, rotting carcass next to him, furiously grabs an ax he had hidden under the bed and uses it to hack up the corpse.
- Disproportionate Retribution: In his Establishing Character Moment to make the audience know hes the biggest asshole ever churned out by Shaw Brothers, Chun-yu is introduced beating up a terrified, crying servant girl as punishment for spilling red bean soup. When his wife, Lady Chan, tries to stop him, Chun-yu beats her up as well for getting in his way, despite knowing fully well that Lady Chan is suffering from tuberculosis.
- Domestic Abuse: Chun-yu, who punished his maids for the pettiest of mistakes and have no qualms abusing his wife who is suffering from tuberculosis. Early in the film it's mentioned that he had "caused nine handmaidens to flee from the mansion because of his abusive nature".
- Driven to Madness: The ultimate fate of Leung Yi-Wah. She didn't die, but being reduced to a trembling vegetable who believes she's permanently haunted by the ghost of the friend she double-crossed and whose murder she arranged is pretty much a Fate Worse than Death.
- Ear Ache: Leung Yi-Wah, at the end of the failed exorcism, ends up having her ears ripped off by Chan Sau-Fong, who is pretending to be her deceased twin's ghost.
- Faking the Dead: At the end of the first act, the semi-unconscious Chun-Yu ends up being shoved into a vat of water by a pissed off Leung Yi-Wah, who then begs for Lady Chan Sau-Ying to help her sit on the vat's lid and drown Chun-Yu, where they then dispose of Chun-Yu corpse together. Except that's not what it seems; truth is, Chun-Yu had a hidden pipe with him, allowing him to breath underwater, arranged by his accomplice Leung Yi-Wah. With Chan Sau-Ying, already suffering from tuberculosis, coupled with the guilt over the supposed murder, Chun-Yu can then "return" as a ghost to force his wife into dying of shock.
- False Friend: Leung Yi-wah to Lady Chan Sau-Ying, who pretends to sympathize with the oft-abused Chan, but is actually plotting for Chan Sau-ying's death — with Sau-ying's unfaithful husband, Chun-yu — in order to claim the Chan family's inheritance.
- Food Slap: One of Chun-yus several Jerkass moments have him throwing his tea in his wife's face because "it's too hot", in a Live-Action reenactment of the Jerkass page image.
- Fan Disservice: The ending sees Yi-Wah, in order to have Lady Chans ghost exorcised from her, being stripped naked, shaved of every hair from her, getting tortured by being burnt alive, and having her body painted with Buddhist scriptures. Complete with a close-up of her nipple being slathered in ink.
- Genre Shift: What starts off as a Foreign Remake of the French movie, Les Diaboliques suddenly takes a turn into supernatural horror territory. Before becoming a mystery whodunnit film.
- Gold Digger: Yeung Chun-Yu, who married himself into the Chan family for their fortune. With some assistance from his lover, Yi-Wah, who's pretending to be Lady Chan's closest friend but is actually after the Chan's inheritance, in the form of millions of dollars' worth of priceless jade.
- Gorn: The onscreen death and gore effects are pretty well done, if not too over-the-top.
- Hate Sink:
- Chun-yu, JUST this guy. The Shaws didnt even bother to hide the fact that audiences are supposed to despise his guts, that they might as well paint the words "despicable piece-of-filth scumbag" on his forehead. In his very first scene he brutally abused a frightened young maid for spilling his soup, and when the sobbing young maid gets comforted by Lady Chan only to have Chun-yu walking in on her, he then continues beating the poor maid. He refers to his tuberculosis-ridden wife as "that diseased bitch" and "sickly waste" and abuses her physically, verbally, and emotionally, with a further scene revealing he had driven away at least nine other maids, all of them young women from poor households only trying to make a living, with his abusive nature. The Reveal later on makes his despicability multiply maybe tenfold, see the next line.
- Leung Yi-wah is introduced as a distant friend of Lady Chan Sau-ying, but is secretly working in tandem with Chun-yu to have Lady Chan already suffering from chronic tuberculosis murdered. Being the secret lover of Chun-yu, Leung Yi-Wah fakes Chun-yus death and have Lady Chan psychologically tormented with guilt, before arranging for her former best friends brutal death, which she shows no remorse over.
- Helping Hands: Lady Chans ghost animates her hand to scare off a priest trying to exorcise her.
- Incurable Cough of Death: On Lady Chan Sau-ying, after her tuberculosis took a turn for the worse. It ends up killing her.
- Impaled with Extreme Prejudice: Chun-yu, after seeing his deceased wife Lady Chan actually Chans twin sister, Chan Sau-Fong appearing in his bedroom, a day after he had hacked her corpse in pieces, ends up throwing himself off a balcony, where he gets impaled on a stone structure.
- Jerkass: Chun-yu, being an abusive wife-beater and Rich Jerk, and a Gold Digger after the Chan family inheritance.
- Karmic Death: Chun-yu, who arranged for a "Scooby-Doo" Hoax that causes his tuberculosis-laden wife to die a slow, agonizing death, ends up being the victim of another hoax arranged by his wife's twin sister, no less which causes him to throw himself to death.
- Manslaughter Provocation: When Chun-yu, having crossed the line by forcefully ripping off Lady Chan's jade bangle, a treasured family heirloom from Chan's mother, just to pawn it for booze money, and tried to beat up Lady Chan's maid and only friend Yi-Wah when she tried to stop him, eventually Yi-Wah ends up knocking the near-drunk Chun-yu into a vat of water and shouting for Lady Chan to help her hold the lid down, drowning the abusive husband for good. Except it was subverted later on when Chun-yu never drowned; he's faking his death as part of an excessively complicated murder scheme to eliminate his tuberculosis-ridden wife for her inheritance.
- Missing Reflection: The ghost of Lady Chan Sau-ying. A laborer talking to her assumes she's a human until he glanced at a nearby mirror and sees himself alone in an empty room.
- The Reveal: Lady Chan Sau-Ying's ghost isn't behind the hauntings which eventually results in the death of her wife-abusing husband, Chun-yu, and unfaithful friend, Yi-Wah; turns out Chan Sau-Ying have a younger sister, Chan Sau-Fong, who arranged for the "haunting" to have the perpetrators behind her death respectively driven to suicide and insanity.
- "Scooby-Doo" Hoax:
- After faking his death, Chun-yu pretends to come back as a malevolent demon in order to scare his wife, Lady Chan Sau-Ying — already suffering badly due to tuberculosis — until she ends up dying horribly from shock and guilt. The moment Lady Chan dies, Chun-yu then shows up, claiming to be returning from a business trip, right in time to hog all the inheritance for himself.
- This ends up biting him back in the ass for as it turns out, Chan Sau-Ying have a twin sister, Chan Sau-Fong, who pretends to be her sister's ghost, and coming back to haunt Chun-yu and Yi-Wah. For instance, when Chun-yu wakes up to find his wife's decomposing body on his bed? Turns out Sau-Fong dug her out of the grave and carried her corpse to the bedroom
- Slipping a Mickey: After Chun-yu's supposed death, Lady Chan Sau-Ying's tuberculosis predictably worsens, with Yi-Wah, her friend and only remaining handmaiden, being the caretaker that serves Chan her medication. Except Yi-Wah is secretly spiking Chan's medicine with hallucinogens and various toxins, allowing Lady Chan to hallucinate seeing her husband's ghost, so that Chun-yu, who never actually died, can then scare Lady Chan to death.
- Vengeful Ghost: Subverted. Lady Chan Sau-Ying's ghost returns after her death, but she isn't vengeful at all, the only thing she did which is to prevent labourers from burning her prized furniture and using an illusion to scare off the priest trying to exorcise her. The spooky stuff is orchestrated by Chan Sau Fong, her twin sister, who creates a hoax in order to have Chun-yu and Lady Yi-Wah, the perpetrators behind her death, brought to justice.