The Terror of the Triangle

A red triangular purse. A discarded set square. A black paper triangle marked with a curse. For one young mathematics student, these are the materials of an experiment: can an ordinary shape become an object of overwhelming dread?

He chooses a nervous stranger and begins placing triangles in his path. But curiosity soon gives way to the pleasure of controlling another person, and the world itself seems ready to multiply his work. Recounted years later, his confession turns a simple geometrical figure into a disturbing question about fear, responsibility and the stories people tell to excuse themselves.

First published in Musen Denwa in April 1927, Unno Jūza’s The Terror of the Triangle is a single psychological horror short story, not a novel or collection. This edition presents a complete, unabridged translation directly from Japanese, with explanatory notes and source information. Japanese names use surname-first order and Hepburn macrons. The translated story contains approximately 5,246 words, excluding editorial matter.