This is based on a play and it shows :all the action tales place in the heroine's house , in a stifling atmosphere in which the ceaseless turning wheel lapping creates a tension ; it is sometimes slow-moving ,but a little humour gets into the lugubrious atmosphere (the gossip woman who phones ; the vicar and the incongruous little help he provides ) and acting is excellent : you can't be wrong with Joanne Woodward ,a character actress who portrays a hostage ,a victim of an escapee from a mental hospital ; little by little ,doubt creeps into one's mind : is she so innocent?Stuart Whitman is credible as well as this lunatic who's seeing things (a dead body on the wheel)and who perhaps might not be really guilty :the circumstances of the crime which sent it to the asylum remain mysterious.
There's of course an unexpected ending ; although it's not as strong as such "in camera " thrillers as Levin/Lumet 's "death trap" , it is an unqualified must for people fond of suspense films.