Today, as he often does, rich kid Martin Durnley (Hywel Bennett) is visiting his brother, who due to being afflicted with Down's Syndrome stays in a special home. As he chats with the doctor in charge, mention is made of possible psychopathic tendencies in the siblings of those who are so afflicted, and Martin drops his cup of tea in an unconscious gesture. This is because he does have such leanings, as can be seen when he goes to a department store and shoplifts a toy duck, which the store detectives blame on him and innocent stranger Susan (Hayley Mills), believing them to be accomplices. Susan manages to persuade them otherwise, but Martin has a trick up his sleeve: he pretends to be simple-minded to charm his way out of the situation, a ruse that he follows when he tries to get to know Susan better...
The late sixties were a funny time for cinema as filmmakers attempted to cater for more adult audiences in more self-consciously daring ways; by the seventies many of them had the hang of it, but before then audiences were treated, if that's the right word, to bizarre efforts like this one from the celebrated British team of the Boulting Brothers. Obviously patterning themselves after Alfred Hitchcock, it's the whistly Bernard Hermann theme that is most recognisable about the project today, as it was used prominently on Quentin Tarantino's Kill Bill soundtrack. That said, there was a measure of notoriety about the film in its day.
This was because of the flimsy excuses the psychopath has for acting as he does. It's absurd to say that the villain's mental unbalance was explained by him being a brother of a Down's Syndrome boy, yet that's what a doctor proposes later on in the film, and understandably there was much protest from those who knew better. For this reason the film starts off with a tacked-on voiceover telling us that basically the science of the story you're about to watch is bullshit, only he puts it in more sensitive terms, which is more than the rest of the tale affords us. We can blame scriptwriters Leo Marks (of Peeping Tom infamy - he couldn't half pick them) and Roy Boulting, the director, working from a story by Roger Marshall for all this.
If you succeed in forgetting the ridiculousness of the premise, then there are compensations. Bennett's Martin is unnerving in the manner he worms his way into librarian Susan's life, using the name Georgie and keeping up his charade to insane lengths, even to the point of moving into the boarding house that she shares with her mother (Billie Whitelaw). Mills is her usual wholesome self, whose well meaning character's nature is exploited, only beginning to cotton on to what's really going on when Georgie forces a kiss on her. Meanwhile, his overbearing stepfather (Frank Finlay) is trying to send him off to Australia, but he has other ideas, ideas involving a sharp pair of scissors. As a thriller, Twisted Nerve's bad taste and committed central performance carry it some of the way, but its determination to shock in a modern style leaves it looking pretty silly decades later. Not that it was particularly sensible back then.