The Smiler and the Knife by Nicholas Blake

In 1935, Anglo-Irish poet Cecil Day-Lewis (1904–1972) wanted to supplement his income by writing a detective novel. He created a pseudonym, Nicholas Blake, and published A Question of Proof. Over the following years, protogonist Nigel Strangeways, amateur investigator and gentleman detective, would appear in sixteen novels. The Smiler with the Knife (1939) “features a Fascist organisation plotting to overthrow British democracy.” [Wikipedia]

Shown here is the cover of an American paperback edition published as Popular Library no. 41 in 1945, with cover art by H. Lawrence Hoffman (1911–1977).