Machiko Sonoda, Ran's computer school teacher and Kogoro's drinking buddy, is found lying still – presumably dead – behind the closed shutter of Beika City Bank's safe-deposit box floor. There is a warning – the moment the shutter is open or the police make a move, the bank will be exploded. When asked for the murder culprit, all three suspects – Yuzo Nimura, Yoko Sakai and Ryosuke Hasegawa – raise their hands. Can Shinichi find the true culprit and prevent the 'explosion'?