The story is about a lustful scholar (played by Lawrence Ng) who dares to challenge the moral teachings of the Sack Monk. The monk attempts to lecture the scholar that spiritual enlightenment transcends the passions of the flesh but the scholar, who enjoys women, naturally doesn't agree. However, the most powerful man in the town marries his daughter, played by Amy Yip, to the Scholar. The daughter is a virgin and has been taught that sex is dirty.
The scholar, after a disastrous yet humorous wedding night, soon initiates his bride into the pleasures of sex, aided greatly by the illustrations of a copy of said sex manual that he owns. But soon, the amorous husband goes about his 'scholastic travels' where he meets the greatest thief known to man. The thief is able to sneak into people's houses undetected, and the scholar wants to learn this skill so that he can sleep with other men's wives. The thief was initially willing to help him, until he catches the scholar one day and discovers that the scholar is not very well-endowed.
The thief tells the scholar that stealing other men's wives requires both good lovemaking skills and equipment. The thief promises to help the scholar only if he has a horse's penis. Of course, the thief didn't think it was possible, until the scholar returned one day, indeed, with a horse's penis attached as his own. Apparently, the scholar met a doctor who was able to replace anatomical parts (a scene with a cameo by Hong Kong funnyman Kent Cheng).
The doctor managed to transplant a horse's penis to replace the scholar's meager one. Armed with his new 20-inch weapon, the scholar goes on a sexual rampage, not caring if he is seducing other men's wives, or is nearly caught in the process. Meanwhile, the scholar's wife, after experiencing the joys of sex, becomes sexually frustrated. She tried masturbating with paintbrushes but is left unsatisfied until she has an affair with the gardener, the husband of one of the wives the scholar seduced. She becomes pregnant and runs away with the man, who persuades her to have an abortion. She soon finds solace in a brothel where she perfects her sexual skills to become the top courtesan.
Meanwhile, the scholar husband, starts to contract an AIDS-like frailty due to too much sex (involving 2 sisters-in-law who are bisexual and into S&M). He goes to the brothel for treatment, where he is offered the top courtesan. At first, both husband and wife cannot recognize each other; she looked at his penis and thought it couldn't be her husband's because his was small; he couldn't recognize her because his eyesight was failing. While they were having sex, he took a close look at her figure and nipple and recognized her. To her dismay, he screamed and shouted and called her a disgrace. To his dismay, she went off and hanged herself. The man, completely broken, went back to the monk to ask for forgiveness.