Returning home to Hong Kong from Canada to surprise her parents with a visit, Kei Po-ehr (Idy Chan Yuk-lin) finds her mother (Tanny Tien Ni) on the verge of a nervous breakdown. Plagued by visions of a ghost child who resents Po-ehr's return, the woman confides in her physician (Kwan Hoi-san), who believes that she is suffering from some form of mental illness. After experiencing some disturbing visions, Po-ehr begins seeing a young and supportive psychiatrist (Tong Chun-chung) and the relationship soon extends beyond doctor/patient, much to the consternation of her old, possessive boyfriend (Mai Te-lo). After an unsuccessful attempt to drive Po-ehr to suicide, the spirit assumes her form and orchestrates murderous havoc in the family via illusion and possession.

One of the few Shaw Brothers features directed by a woman (Angela Mak Leng-chi), THE SIAMESE TWINS is a plodding misfire that wastes much of its running time on a pair of largely immaterial secondary characters. These supposed friends of Po-ehr are teeth grindingly obnoxious and present simply to pad out the scant storyline. There is a half-hearted attempt to shroud the early scenes in mystery but, thanks to the title and a narrated prologue (which features images of real-life birth defects), we already know almost exactly what is coming. The only notable horror elements are confined to the last reel and viewers expecting anything along the lines of SISTERS or BASKET CASE will be very disappointed as there is only a smattering of gore, hardly any inventiveness (would you believe the umpteenth ghostly little girl with a white ball?), and a very weak twist ending. If you must watch, try and figure out how HK censors could justify giving this the adults-only Category III rating because of some nudity during consensual sex, while THE KILLER SNAKES (which is filled with rape, torture, and graphic cruelty to animals) merits only a IIB or PG-13!