Martin Durnley (Hywel Bennett) lives at home with his over-protective mother (Phyllis Calvert) and stepfather (Frank Finlay), who is worried about his lack of motivation.
When they try to send him to Australia to take a job, Martin says he’s going to Paris but goes to stay at the boarding house run by the mother of Susan Harper (Hayley Mills), a pretty young librarian he met in a toy shop when he stole a toy duck.
As “Georgie Clifford” he pretends to have learning difficulties and Susan and her kindly mother, Joan (Billie Whitelaw) treat him like a child.
But Martin is a psychopath and one night he sneaks out of the house and murders his stepfather.
Susan finds out who he really is (the copy of Psychopathia Sexualis in his room is a bit of a giveaway!) and goes home to warn her mother but Martin has already killed her.
Martin shoots himself and the police arrive to find him dying at Susan’s feet.
The movie reunited Bennett and Mills with director Roy Boulting who also directed the young artists in The Family Way (1966).
Martin Durnley (Georgie Clifford)
Sir John Forrester
Detective Sergeant Rogers