The body of Kadowaki Eiji is discovered in Beika Park with his head split open. Eiji was the problem child of the Kadowaki family. According to rumor, Eiji abused his mother Yasuko, and his older brother Yuichi would try to stop him. It also becomes clear that a suspicious man was investigating the Kadowaki family. Inspector Megure suspects Yuichi, but Yuichi has an alibi for the time of the crime. Later, they learn the suspicious man was Takase, a student of former grade school teacher Yasuko. The police go to question Takase, but...

Kogoro, Conan, and Ran are invited to dog food company president Anna's birthday party and arrive at the yacht harbor. Shortly after the party begins, Anna is shot to death by a masked man wielding a shotgun. Inspector Megure questions vice president Inamura, director Machiko, and secretary Morishima, and Anna's ex-boyfriend Hyodo emerges as a suspect. However, Hyodo has an alibi: he was robbing Anna's apartment. Kogoro and the police suspect he fabricated his alibi.