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
Chico and Rita the others escape. Rita and Chico leave the rest of the party and go to a bar where Chico introduces her to bebop music, which she takes up quickly. Afterwards they go to Chico's place and spend the rest of the night together. The next day Rita wakes up to find Chico playing a new composition on the piano, which he names "Rita". As they play and kiss, Juana, Chico's former girlfriend, walks in and picks a fight with Rita. The two women angrily leave Chico, feeling betrayed. However, Chico is still smitten with Rita and begs Ramon to convince