Mr. Yukimura is killed in a car crash in Hakone. The police wonder why he was there because he was supposed to be in Kyuushuu then. Mr. Yukimura's daughter, Michiko, and her elder brother go to the place where the car crash happened. The place is full of a scent that Michiko or her brother doesn't know.
Naomi is Michiko's classmate. Naomi's elder sister and Michiko's elder brother have been engaged. Naomi's father works for the same cosmetic company as Mr. Yukimura did. He is very surprised to hear Mr. Yukimura died. Naomi finds a bottle of perfume in his pocket. He says it's a perfume that he is now developing.
Naomi and Michiko go to Ginza, where the cosmetic company is located. Naomi looks into the company with a telescope and sees her father discard perfume and tear up some papers. Naomi asks Michiko's elder brother, who also works for the cosmetic company, to take her to the company. Naomi finds an empty bottle labeled "Kurosuisen"(Black Narcissus) and torn papers in a trash can. Michiko's brother recognizes the smell. The same smell was floating at the place where his father died.
Naomi finds Mr. Yukimura's diary and her father's letter in Mr. Yukimura's study. The letter says Naomi's father will meet the president of the company in Hakone to talk about Kurosuisen. The date and time when Naomi's father would be meeting the president were exactly the same as those when Mr. Yukimura died. Naomi secretly takes Mr. Yukimura's diary home. Naomi's father finds it in Naomi's room.
Naomi's father tells her the truth. He developed a perfume called Kurosuisen. It had artificial ingredients but smelled so nice that anybody believed it had natural ingredients. Naomi's father wanted the price of it to be 1000 yen a bottle. However, Mr. Yukimura suggested the price should be 4000 yen a bottle. Mr. Yukimura wanted Naomi's father not to let the president know the actual manufacturing cost. He wanted to cheat the company to get money. Mr. Yukimura was driving in Hakone because he wanted to prevent Naomi's father from telling the president about the perfume. Even though Naomi's father didn't mean to kill Mr. Yukimura, he feels guilty.
Naomi's father tells the president about Kurosuisen. The president decides to sell a bottle of it for 4000 yen. He says that the higher the price is, the better it will sell because customers tend to think expensive cosmetics are better than cheaper ones.