Incestuous twins Jacki (Judy Geeson) and Julian (Martin Potter) fall into the Swinging London scene during a break from university. The pair see Jacki’s stuffed teddy bear, Agamemnon, as a father figure and often speak to him as if he were a real person.
Jacki meets Clive Landseer (Alexis Kanner) at a party and instantly takes a liking to him, which makes Julian jealous as he wants Jacki all for himself.
When Jacki leaves with Clive, Julian begrudgingly tags along with Clive’s sometimes girlfriend, Denise (Marian Diamond), although he gets drunk and angry.
It becomes apparent that Clive is a complete scumbag. He is, in fact, a pimp and conman who owes gangster Rod Barstowe (Mike Pratt) a lot of money and sees the rich, spoiled, and sheltered twins as an easy solution to his predicament.
Clive drugs Julian and takes him to visit his prostitutes, who turn out to be transvestites. He has two of them rape Julian while he photographs the encounter, planning to blackmail him for the money he needs.
Denise warns Jacki, and the twins concoct a plan of revenge.
Dressing up in bedsheets with only their eyes showing, they challenge Clive to tell them apart before stabbing him to death with an ornamental sword.
Jacki’s teddy bear Agamemnon is cut in half during the incident, causing her to suffer something of a mental breakdown.
Jacki disappears and develops amnesia but is rescued by kindly Conservative MP James Harrington-Smith (Michael Redgrave) and rests at his home while the police go on a manhunt for the twins.
The startling downbeat ending packs a very potent punch.
The original soundtrack album became a cult classic and enjoyed far more popularity than the movie. Released in some markets as Twinsanity.
Detective Inspector Kingsley