This is very dated and very much of its time (a capsule of the 'swinging sixties). Strangely set bound (even the exterior scenes are filmed on a set), it has the appearance / atmosphere of a stage play. For such a distinguished cast, there are more than a few shaky performances which makes the direction suspect. Not particularly enjoyable as a thriller, certainly not scary and why the DVD still carries an 18 certificate in the Uk heaven only knows. On any night of the week you can watch more explicit material than this on the main TV channels. Only worth watching as a curiosity now I'm afraid. One thing's for sure, Hywel Bennett would certainly have been better keeping his clothes on in the film, his pasty body isn't a pretty sight!
Review of Twisted Nerve
