Hasumi Kayoko, the rookie investigator at the all-female Hasumi Detective Agency, always observes people and cases in a level-headed manner. She detests lies and secrets, and has a strong sense of justice. Her late father worked at the city news desk of a newspaper, but committed suicide 7 years ago. However, the truth lies in darkness and Kayoko's mother, Kyoko, the agency's director, has been secretly pursuing the facts. An incident becomes the catalyst that entwines Kayoko and the people around her, and she closes in on the truth behind her father's death.