Kotou no Oni

Kotou no Oni manga summary: An adaptation of Edogawa Ranpo's eponymous novel. It's Tokyo and the year is 1924. A young tradesman by the name of Minoura Kinnosuke finds his fiancée murdered inside a locked room. As he struggles to find the culprit, a doctor by the name of Moroto Michio, who has long harboured unrequited feelings towards Minoura, offers to help solve the case.