His first whodunnit novel, published in 1936, was The Doctor Died at Dusk. Written under an English-sounding and, in the future, often used nom de plume, Geoffrey Holmes, it featured journalist Robin Bishop. In his 1938 Then There Were Three, Mainwaring summoned up a new investigator, the milk-drinking, accordian-playing private detective Humphrey Campbell. Four years later, in The Street of Crying Women, he introduced Hispanic cop, Jose Manual Madero, a Zapotec Indian who knits socks and smokes cigarettes after flipping them in the air and catching them between his lips. Robin Bishop would go on to feature in The Man Who Murdered Himself (1936), The Man Who Didn't Exist (1937) and The Man Who Murdered Goliath (1938).
from Heartbreak and Vine: The Fate of Hardboiled Writers in Hollywood by Woody Haut (2002)