The Red Triangle: Being Some Further Chronicles of Martin Hewitt, Investigator

A series of linked detective tales records an investigator's methodical pursuit of a criminal network identified by a curious red triangular mark. Told by a companion narrator, the episodes recount thefts, murders and burglaries—most famously the case of Samuel's diamonds and a strangled clerk—whose scattered clues gradually reveal an organised conspiracy. The narratives combine close attention to physical evidence, house-to-house inquiries, and police cooperation, tracking how small details such as keys, back doors and disguises expose a larger, concealed criminal scheme and ultimately allow the detective to unmask its workings.