Who wrote the book that Peggy Robertson's 1948 movie is based on?
Peggy Robertson: Margaret "Peggy" Robertson (née Singer; 13 September 1916 6 February 1998) was a British-born script supervisor and personal assistant to Alfred Hitchcock from the 1940s through the 1970s during which time she worked on the films "Under Capricorn" (1948) and "Stage Fright" (1950), "Vertigo" (1958), "Psycho" (1960), "The Birds" (1963), and all of the director's remaining films. Under Capricorn:  The film was based on the novel "Under Capricorn" (1937) by Helen Simpson, with a screenplay by James Bridie.
Helen Simpson