Kyoka, a university student, receives an old brown envelope in which she finds a photograph of her classmate, Sachiko. With this, she also finds a mysterious message saying "Help me". One day, while at a café, Kyoka overhears that "somebody had been spirited away by a man in a black suit". It was at that moment that Kyoka recalled the moment that Sachiko had suddenly disappeared in the mountains right in front of her very own eyes.

在咖啡店打工的大学生山本京香（小出早织 饰）某天收到一封神秘来信，信中附有一张她小学三年级时和同学幸子在山顶的合影。京香对当时的情景毫无印象，而在照片背面则发现“救命”二字。心存疑惑的她返回家乡，却得知幸子于10年前便已失踪。为何京香不记得当年的事情？回忆中不断 闪回出现的黑衣男子又是谁？