While on a trip with the Detective Boys and Prof. Agasa, Conan spots a strange group of people on the roof of a nearby building with his binoculars. He witnesses a suspicious test shooting with his friends where it seems that a very skilled sniper is being held at gunpoint by some men and forced to shoot a particular target, with his grilfriend being held hostage. Now Conan and his friends must decode the message the sniper left on a calculator in order to help him.