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 (film) four out of five stars. He describes Walters's "splendidly rich interpretation" of Rita and characterises her "reactions to the traditions of English lit[erature] [as] carry[ing] the caustic brilliance of true intelligence, a shattering of blithe pretension". Of Walters and Caine, Nathan opines, "they make a beautifully odd couple, in a love story at one remove". This reviewer depicts the director's effort as "effective, and finally optimistic," and observes about the film that the playwright's "angry message that people are trapped by their environment not their abilities, is salved by the sweetness of [Frank's and Rita's] final parting." Nathan's "verdict" of