Conan witnessed a policeman who was on the phone being shot in the rain on the street, and hurriedly tracked down the murderer, but the murderer escaped. The dead man closed his eyes and grabbed his left chest, which seemed to be a hint. Afterwards, Conan learned from Officer Megure that grabbing the left chest was a hint that there was a police manual there. Soon another policeman was shot in the underground garage with a police manual in hand. Regarding these two cases, Officer Megure and others were uncharacteristically unwilling to reveal too much information to Maori Kogoro and Conan. Maori was unwilling to ask further, and Officer Shiratori only replied "Need not to know". This sentence is a secret language used between police officers, which means that these two murders are related to police insiders. Conan, Xiaolan and others attended the wedding banquet of Shiratori's sister, and the power suddenly went out. At that moment, Xiaolan was in the bathroom with policewoman Sato. When Xiaolan picked up the flashlight beside her to illuminate, a bullet shot into Sato's body, and Xiaolan fainted. The next day, Xiaolan woke up, but she blamed herself for causing Sato to be shot and lost her memory. Seeing that the situation was getting worse, Megure told the secret that the two dead policemen were investigating a case involving the suicide of doctor Nino with Sato, and the case involved the son of the police chief. When Conan assumed that the son of the police chief was one of the suspects, he also thought of the two people missing from the banquet after Sato was shot.