Itō Ken (1895-1945), a proletarian writer, stated in 1930 that his collection of short stories Shanhai Yawa (Shanghai Night Stories) was intended to be a “detective and proletarian like popular novel.” But how can a proletarian writer with a Marxist worldview change an apolitical genre such as the detective story into a weapon of proletarian literature? Could a Marxist detective reveal the crimes of capital? Examining Itō's journalistic articles and fiction within the context of mass media and detective fiction, I aim to show how Itō Ken tried to rework the detective genre into a form of proletarian literature.