While traveling home on the Shinkansen from Osaka, Conan, Ran, and Kogoro ran into Officers Sato and Takagi, who were transporting a criminal. Later, a bomb was found on the train which Officer Sato went to investigate. At that time, while she was in the bathroom with it, Officer Takagi had to take the criminal to the bathroom. And then, he apparently committed suicide but...
Kogoro has been invited to a detective meeting by an unknown assailant who sends him money. There are six detectives there excluding Conan. They are in a house where a massacre happened years ago. One of the detectives are killed and they are stranded in the mansion as the bridge has been cut and the cars have been burned. It also appears that the unknown assailant is using the name Kaitou Kid.
Senma and Ogami were co-conspirators and had arranged for the detectives to arrive in an attempt to have them find the treasure for them. Senma's archaeologist father had disappeared looking for the treasure, so she wanted to know what the treasure was at all costs. Sensing that Ogami's greed had got the best of him and that he would kill her after they had found the treasure, she poisoned him using his nail biting habit. She had planned to fake her death, have the other detectives find the treasure and then have them kill each other, but they were not fooled. All the detectives who killed each other are alive all along.
Instead, she is tricked into confessing to Conan, who reveals the true secret of the treasure: the entire mansion is actually made of gold. After solving the case, Kogoro was revealed to be Kid in disguise and escapes before Conan could capture him.
