“I will remember. The person who ‘killed’ you, my precious friend.” Haruka Ando was caught up in a series of murders during her school festival in high school, losing her best friend and falling into a coma herself for ten years. After waking, Haruka began working at a detective agency. When she met a young man named “Irie” who worked there, a sudden flashback filled her mind: the day of that incident, when a male classmate had proposed, “If we're both single in ten years, let's get married.” From that day on, Haruka encountered numerous difficult cases together with Irie. And lurking behind these cases was a mysterious new drug, “Snow White” Will Haruka be able to track down the culprit behind that incident? And what will become of her promise with “him”?