A great detective who appears out of nowhere and solves cases with brilliant deductions. Kirinomiya Saika, who acts like this, is my senior. She’s the daughter of a conglomerate, not someone that an ordinary student like me can approach, but for some reason I’m being made her assistant. As I’m dragged along to crime scenes, a real mu*der case finally occurs. “The mystery that wanders in the depths of darkness, I will expose it to the light of day.” No matter how much my senpai shows off her deductions, she cannot solve the mystery.