Conan gets to watch over a two year old kid which names itself Santa. Ishikawa Shigeko, Santa's Mother, has been pushed down the cross-walk stairs. She is uninjured but mentioned to Kogoro Mori that in the last days she got the feeling that she is being watched by someone. She asks Kogoro to find out who is watching her. But in the middle of the investigation Ishikawa is kidnapped.

At the theatres, the Detective Boys run into Shiratori who is depressed Sato's affection is being directed at Takagi. Shiratori reveals that he is bind to Sato because of an encounter he had with her in the past. Shiratori explains Sato as a young girl stood up to two thieves by herself. Shiratori helps her stop the thieves and in return receives from her a drink with paper folded sakura. Conan questions whether that girl was actually Sato as their personalities differ greatly. During the movie, Shiratori runs into a woman named Nami Kasakura who offers him a drink with paper folded sakuras causing Shiratori to consider the possibility she was the girl in the past. After the movie, Kasakura tells Shiratori she is being stalked and asks him to investigate. At her apartment, Kasakura's boyfriend is found dead. Conan suspects Kasakura but her alibi supposedly states she was at the theatre the whole time.