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) relationship"; he said Russell's screen adaptation "added mistresses, colleagues, husbands, in-laws, students and a faculty committee, [that were] all unnecessary" and said the playwright/screenwriter "start[ed] with an idealistic, challenging idea, and then cynically tr[ied] to broaden its appeal". In 1999, the film was among the BFI Top 100 British films. In 2007, while promoting the remake of "Sleuth", Caine called "Educating Rita" "the last good picture [he] made before [he] mentally retired." The film was released on DVD in the UK and the US. ITV Studios released the film onto Blu Ray in the UK (Region B) in 2008 as