A former classmate of Kogoro Mouri, who is now a sergeant, telephoned inviting the Mouri family to go barbecue at his home. Conan is also glad to go with them.
The next day, when they are eating in the garden, Conan notices something abnormal of the sergeant, for he would not drink even a little beer though he says command may be granted even on holiday. What*s more, he keeps on looking at his watch, as if he is waiting for something. Then the mobile phone of the sergeant rings. A membership of a sinister gang killed a person and is about to escape. The sergeant intends to go by himself. Kogoro Mouri suggests since he is on vocation and has no pistol, he should either call the police headquarters or let him go together. The sergeant allows Mouri to go with him and goes back into the room to put on his coat. After a while, he goes out. When he steps into the car, Conan hears a slight mental striking sound from his ankle.
The sergeant and Mouri drive away. It seems Conan thinks of something. So he and Ran catch a taxi to pursue them, leaving the sergeant*s wife worried.
When they arrive, the sergeant has gone to meet the murder on his own. At that time, a gunshot is heard and the murder is dead. Later, the sergeant explained that when he intended to seize the pistol from the murder, the murder mindlessly shoot himself.
The pistol is examined, another fingerprint is found besides the sergeant's and the murder's. Conan memorises the strange behavior of the sergeant. He also finds an empty videotape cassette with a piece of wet cloth on which the smell of oil is found. The answer is clear. According to Conan's reasoning, the sergeant receive the call from the murder several days ago, and he asked the murder to call him at that time in order to let Mouri know. He tied the pistol at his angle and killed the murder with it. The evidence is the third fingerprint on the pistol. The sergeant's wife may have found that pistol for a time, but she kept silence for that. The fingerprint is hers.
The sergeant admitted all the fact. Talking about the motive of killing, he admits that he was bribed by the sinister gang, and provided them with information about the police. When he received a threat several days ago, he decided to kill him.