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
Willy Haas Willy Haas Willy Haas (6 July 1891 – 4 September 1973) was a German editor, film critic, and screenwriter. He wrote for 19 films between 1922 and 1933. He was a member of the jury at the 8th Berlin International Film Festival. Willy Haas was the son of a Jewish lawyer. He studied law himself, and at a young age joined a literary circle with his friends Franz Werfel, Paul Kornfeld and Johannes Urzidil. He had personal contacts with Franz Kafka and Max Brod. This circle, which met in Prague at the , also included Ernst Polak, the husband of