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
Rita Sullivan happy with her work. Hilda insinuates that Alan is seeing Rita and is sacked by Alan. Hilda tells Elsie she was sacked because she knew too much about Alan and Rita. Elsie decides to ask Rita what's going on. Rita tells Elsie there's nothing between Alan and her - it's the booze she's got to worry about. On Christmas Day, 1972, the residents gather in the select of the Rovers for the 40's show as Rita plays Marlene Dietrich. Len is appointed Deputy Mayor. Rita avoids Len. He gives her an invitation via Jerry for a private drink. Jerry tries