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
Amanda Muggleton all the State and commercial theatre companies. On stage, her performances with State theatre companies include "Privates on Parade", "The Matchmaker", "The Seagull", "Shirley Valentine" (MTC), "Master Class", "Nicholas Nickleby", "The Rise and Fall of Little Voice", "Soulmates" (STC), "Duet for One", "The Winter's Tale", "Gigi", "We Were Dancing" (QTC), "Twelfth Night", "Blithe Spirit" (SATC), "Educating Rita", "Medea" and "Shirley Valentine" (Hole in the Wall, Perth). Muggleton's commercial credits include "HMS Pinafore" (Essgee), "Hello Dolly" (The Production Company), "The Book Club", "Master Class" (ICA), "Annie" (GFO/SEL/Macks), the original "Steaming" (Morley, Davis), "Eureka!" (Essgee) and "Losing Louis" (Ensemble Theatre). Muggleton has