Question: Who wrote the book that Peggy Robertson's 1948 movie is based on?

Context paragraphs:
Whispering Smith (TV series): Whispering Smith is an American Western series that originally aired on NBC.  It has the same ultimate source material as the 1948 movie of the same title (and some other films), but differs in some significant respects.

Under Capricorn: Under Capricorn is a 1949 British historical thriller film directed by Alfred Hitchcock about a couple in Australia who started out as lady and stable boy in Ireland, and who are now bound together by a horrible secret.  The film was based on the novel "Under Capricorn" (1937) by Helen Simpson, with a screenplay by James Bridie.  It was adapted to the screen by Hume Cronyn.  This was Hitchcock's second film in Technicolor, and like the preceding color film "Rope" (1948), it also featured 10-minute takes.

Anna Robertson Brown Lindsay: Anna Robertson Brown Lindsay (1864–1948) was the first woman to earn a doctorate at the University of Pennsylvania.  She wrote a number of books on theological topics, most of which were published in the early-1900s.  Anna Robertson Brown Lindsay was the daughter of a Presbyterian minister and the first woman to graduate with a Ph.D in English from the University of Pennsylvania.

Cliff Robertson: Clifford Parker Robertson III (September 9, 1923 – September 10, 2011) was an American actor with a film and television career that spanned half a century.  Robertson portrayed a young John F. Kennedy in the 1963 film "PT 109", and won the 1968 Academy Award for Best Actor for his role in the movie "Charly".  On television, he portrayed retired astronaut Buzz Aldrin in the 1976 adaptation of Aldrin's autobiographic "Return to Earth", played a fictional character based on Director of Central Intelligence Richard Helms in the 1977 miniseries "", and portrayed Henry Ford in the 1987 "Ford: The Man and the Machine".  His last well-known film appearances were in 2002 through 2007 as Uncle Ben in the "Spider-Man" film trilogy.

Instauration: Instauration was a monthly magazine published from December 1975 through February 2000, ending with volume 25, issue 3.  It was published by Wilmot Robertson (Sumner Humphrey Ireland), who also wrote "The Dispossessed Majority" (1973) and "The Ethnostate" (1992).  "The Dispossessed Majority" was decried as a white supremacist book when notice of it was mailed to students at the Marist School and the Lovett School in 1987.  The magazine and Robertson's books share much in common.  The editorial office of Instauration was in Cape Canaveral, Florida, and the publisher was Howard Allen Enterprises, Inc.

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.

W. Bruce Cameron: William Bruce Cameron (born 1960 in Petoskey, Michigan) is an American author, columnist, and humorist.  Cameron is most famous for his novel "A Dog's Purpose", which spent 52 weeks on the "New York Times" bestseller list and is the first book in a two book series that concludes with "A Dog's Journey".  The book is the basis for the movie version starring Dennis Quaid, Britt Robertson, Peggy Lipton, K.J. Apa, Juliet Rylance, Luke Kirby, John Ortiz and Pooch Hall, an Amblin Entertainment/Reliance Entertainment/Walden Media release in theaters January 27, 2017.

Joseph Knight (novel): Joseph Knight is a historical novel by Scottish author James Robertson published in 2003 by Fourth Estate.  It was the Saltire Society Scottish Book of the Year in 2003 and won the Scottish Arts Council Book of the Year Award in 2004.  The novel is based on the true story of a slave brought from the Jamaica to Scotland, and the novel revolves primarily around the cities of Dundee, near where Robertson was then living, and Edinburgh.

A Dog's Purpose (film): A Dog's Purpose is a 2017 American comedy-drama film directed by Lasse Hallström and written by W. Bruce Cameron, Cathryn Michon, Audrey Wells, Maya Forbes and Wally Wolodarsky, based on the 2010 novel of the same name by Cameron.  The film stars Britt Robertson, KJ Apa, Juliet Rylance, John Ortiz, Kirby Howell-Baptiste, Peggy Lipton, Dennis Quaid and Josh Gad.

Kirk Alyn: Kirk Alyn (born John Feggo Jr., October 8, 1910 – March 14, 1999) was an American actor, best known for being the first actor to play the DC Comics character Superman in live-action for the 1948 movie serial "Superman" and its 1950 sequel "Atom Man vs. Superman", as well as Blackhawk from the "Blackhawk" movie serial in 1952, and General Sam Lane in 1978's "Superman: The Movie".

Supporting paragraphs: Peggy Robertson Under Capricorn
Answer: Helen Simpson