He made his real mark, however, with a string of hard-boiled mystery novels (mostly with small-town California settings), the first of which was The Man Who Murdered Himself (1936).
[2]By the time Out of the Past appeared Mainwaring had already begun to devote himself exclusively to screenwriting, first under the Homes pseudonym and later under his real name.
[1] Other notable credits during this period include The Big Steal (1949, directed by Don Siegel) and This Woman Is Dangerous (1952, with Joan Crawford).
His first important film works bearing his real name were the 1954 shot-on-location crime thriller The Phenix City Story (1954) and the original version of Invasion of the Body Snatchers (1956).
In 1960, Mainwaring was hired by fantasy-film producer-director George Pal to write the screenplay for the MGM Studios film Atlantis, the Lost Continent, released in 1961.