A pop-up book and pink smartphone are delivered to the Mori Detective Agency. In the pop-up book are warnings of a series of explosions. The riddle for the location of the third bomb is "the middle of 7." Conan and his friends think of things expressed in sevens and what the middle of those things might be. In a week, it's Thursday. In a rainbow, it's green. In a musical scale, it's fa. Overwhelmed by the number of possibilities, Kogoro holds his head in his hands. At the police station, they begin searching for places, companies, and schools corresponding to Thursday, Green, and fa, but Conan reasons that Hirukawa's target lies elsewhere...

With all of the possible suspects having no blood on them, Conan and Heiji quickly discover the method used. Now they need to discover the motive.