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 Bennett Dexter Morgan's girlfriend. It is revealed early on that Rita was physically and sexually abused by Paul Bennett (Mark Pellegrino), her ex-husband and the father of her children, Astor (Christina Robinson) and Cody (Preston Bailey). Dexter's sister Debra Morgan answered a domestic violence call and saved her life. Rita, who is ignorant of Dexter's secret life as a serial killer, appears regularly throughout the first season as his main source of support. She plays a much larger role in the episode "Return to Sender", in which Paul is released from prison and demands to be at Astor's birthday party. Rita