John Harrington (Stephen Forsyth) is a handsome, 30-year-old man who in a voice-over narration, claims to suffer from Oedipus complex. He is also impotent and feels compelled to murder young women wearing bridal gowns to remember details of a traumatic event that twisted his mind as a child. Harrington lives in a spacious villa outside Paris, France where he's the manager of a bridal dress factory which is managed by his older wife Mildred (Laura Betti). Despite the image he puts upon himself, Harrington relies on Mildred for emotional and financial support. On one particular morning, the ill-matched couple engaged in a verbal sparring match at the breakfast table. Harrington brings up talk of divorce. But Mildred will hear none of that. After walking away from the argument, Harrington retreats into his office, where he meets Helen Wood (Dagmar Lassander), who has come to apply for the job "vacated" by one of the models who has mysteriously disappeared. Harrington is impressed by her intelligence and beauty, so he hires her on the spot.
Later that night, Harrington lures Alice Norton (Femi Benussi), one of the models at the salon, to his office and takes her to a secret room where he stores wedding dresses. As Alice is planning to leave the salon to be married, he offers her a choice to any of the dresses. She selects one and changes into it as per John's request, after which he hacks her to death with a meat cleaver. Harrington's method for disposing of the dead bodies of women he kills at his office is ingenious: he burns the bodies in the furnace of his greenhouse, using the ashes as a special kind of fertilizer.
The next morning, Inspector Russell (Jesus Puente) arrives to question Harrington about Alice's disappearance for her fiancée reported that she never came home last night. Harrington replies that she left at the end of the day, and has not seen her since. With six models having disappeared from his bridal salon, Harrington naturally has become the prime suspect by the police. But with a lack of hard evidence, Inspector Russell leaves without arresting him, so Harrington is able to continue his killing spree with little difficulty.
Over the next few days, Harrington falls in love with Helen after taking her out to dinner and having casual conversations with her, which makes him very confused. Harrington clearly has no desire to kill Helen, but his contemptuous wife, Mildred, is a constant irritation to him. After Mildred confronts Harrington and accuses him of being unfaithful after seeing him with coming home from a dinner outing with Helen, Harrington decides to retaliate by killing her. Though he does not understand why, Harrington needs to have a wedding dress in his immediate vicinity when he kills. Rather than talk Mildred into putting on the dress, he dons the veil himself. Despite Mildred putting up a fight, she gets hit with the cleaver and falls dead.
Harrington initially buries his wife in the grounds of the greenhouse, but in a surprising twist and much to Harrington's consternation, Mildred's ghost begins to haunt him in an unsusual way; instead of Harrington seeing his wife's ghost, it's everyone who sees Mildred in public, very much alive, but Harrington cannot see or hear her. Thinking that she is still alive, Harrington checks the grave in his greenhouse. The body is still there, so Harrington burns Mildred's remains in the furnace. Harrington takes the ashes and keeps them in a handbag for himself.
Mildred's ghost continues to haunt her husband, appearing only to other people, and not to himself. When Harrington attempts to murder another woman, he is foiled from doing so. Harrington finally decides to murder Helen as a substitute. He lures Helen one night to the same concealed room where he murdered Alice and a few other models. After convincing Helen to change into a wedding dress, he sorrowfully tells Helen that he never wanted to hurt her, but he wants to "fit this last piece into place." He then strikes at Helen with the meat cleaver, but she successfully avoids the blow. But the initial surge of dealing the blow finally gives Harrington the information he needs.
In a flashback, Harrington, as a young boy, adored his mother. When his father died, he became the man of the house and looked after her. However, when his mother remarried, he became miserable. Spying on his mother and stepfather having sex, he became enraged and killed them both with a hatchet. The sight of his mother drenched in blood made his mind snap. Young Harrington apparently tricked the police into thinking a homicidal maniac killed his mother and stepfather, in which he also had subconsciously pushed the entire event out of his mind. Now that it has all come back to haunt him, he is reduced to tears.
In another ironic twist, Helen runs from the grieving Harrington and lets Inspector Russell and a team of policemen into the hidden room where they place him under arrest. It turns out that Helen is a uncover policewoman who was hired by Russell to keep an eye on Harrington. Helen is shaken by her brush with death, but recovers quickly.
After confessing everything, Harrington is loaded into a police van with two policemen escorting him. As Harrington settles back in the police van on its way to jail, he finally realizes that now he knows everything, he is finally free. But then Mildred's ghost appears beside him in the van. But this time, it is only Harrington who can see or hear her. She tells him that now they will be together forever, "first in the insane asylum, and then in Hell for all eternity." Harrington goes berserk with terror, and has to be restrained by the two policemen. Harrington calms down when he realizes that there is no way now for him to avoid his fate.Stephen Forsyth - John Harrington
Dagmar Lassander - Helen Wood
Laura Betti - Mildred Harrington
Jesus Puente - Inspector Russell
Femi Benussi - Alice Norton
Antonia Mas - Louise
Alan Collins as Vences
Gerard Tichy - Dr. Kalleway
AllMovie called it "not the best of Mario Bava's work", but "a must see for those who love the genre and admire stylish horror films."
Although the film does not have enough reviews for a Rotten Tomatoes rating, the site records two positive and two negative reviews from critics.
Tim Lucas, author of the critical biography Mario Bava: All the Colors of the Dark, calls Hatchet For the Honeymoon "Mario Bava's most personal horror movie" and states "Time has shown the film, initially misunderstood and considered one of Bava's lesser works, to be startlingly prescient, pointing the way for Mary Harron's film of Bret Easton Ellis' American Psycho in particular."