mystery writer; detective fiction writer; crime author
Refers to an author who writes mystery, detective, or crime fiction. A straightforward compound of 推理 (reasoning/detection) and 作家 (writer/author).
彼は有名な推理作家だ。
He is a famous mystery writer.
その推理作家の新作が来月発売される。
The new work by that crime author will be released next month.