[5][6][7] Edgar Marsh, a shy librarian obsessed with erotica, becomes infatuated with his neighbour Betty Clare when he sees her undressing in her bedroom.

The shoestring sets and lighting, in fact, contribute enormously towards achieving the correct oppressive aura of dank, seedy, gaslit Victoriana.

Excellent playing by Laurence Payne, Adrienne Corri and Dermot Walsh, from a script which concentrates intelligently on establishing a credible triangle relationship before moving into the horror, creates three-dimensional characters of real interest.

There are, to be sure, one or two purely conventional horror-film gimmicks – lightning zigzagging across the sky at a moment of crisis – but on the whole it is done imaginatively (if not very originally) rather than crudely.

The tell-tale heart itseif is particularly effective, where the whole house – the pendulum of a clock, a dripping tap, a ticking metronome, a swinging chandelier, a piece fallen from a chess-board and rolling gently back and forth – seems to pick up and magnify the terrifying beating rhythm which haunts Edgar.