Daniel Mainwaring (aka Geoffrey Homes) (July 22, 1902 – January 31, 1977) was an American novelist and screenwriter. A native of Oakland, California, he began his professional career as a journalist for the San Francisco Chronicle and enjoyed a successful career as a mystery novelist (under the name Geoffrey Homes). He worked as a film publicist and eventually abandoned fiction for a successful career as a screenwriter.

His first novel (and the only one he ever published under his own name), One Against the Earth, was a proletarian novel about a young man born on a California ranch who becomes a drifter and is eventually unjustly accused of attacking a child, was published in 1932. 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).

His final published novel, Build My Gallows High (William Morrow & Co., 1946), is generally regarded as his best—and its adaptation (by "Homes" himself) into the film noir classic Out of the Past assured his place in film history. Mainwaring explained to interviewer Pat McGilligan that he regarded the novel as a departure from his earlier literary efforts:

With Build My Gallows High, I wanted to get away from straight mystery novels. Those detective stories are a bore to write. You've got to figure out "whodunit". I'd get to the end and have to say whodunit and be so mixed up I couldn't decide myself.

(Wikipedia)