The Riddle of the Sphinx (Inside No. 9) was characterised by Pemberton as a thriller in the style of Anthony Shaffer's 1970 play "Sleuth", while Shearsmith identified the episode as particularly theatrical, in the style of "Sleuth" and Ira Levin's 1978 play "Deathtrap". BBC executives, according to Shearsmith, saw the episode as a cross between "Sleuth" and Willy Russell's 1980 play "Educating Rita" that read as if it had been authored by psychopaths. The executive producer Jon Plowman suggested that the first half of the episode plays out like a radio play. The word-play and tea-drinking in this part of the episode are, in the writers' opinion, very
Educating Rita Bryant. Susan (who initially calls herself Rita), dissatisfied with the routine of her work and social life, seeks inner growth by signing up for and attending an Open University course in English Literature. The play opens as 'Rita' meets her tutor, Frank, for the first time. Frank is a middle-aged, alcoholic career academic who has taken on the tutorship to pay for his drink. The two have an immediate and profound effect on one another; Frank is impressed by Susan's verve and earnestness and is forced to re-examine his attitudes and position in life; Susan finds Frank's tutelage opens doors