The Detective Boys meet Nanami Kyoudou, who's grandfather, Seitarou Kyoudou is the one who built "The Black Tower", rumored to have no entrance and treasure hidden within. Later, they visit her house.

Kogoro prepares to meet with the client Kei Katshitsuka. While waiting, he receives mail of Katshitsuka who changes their meeting location to a local restaurant. There, Kogoro realizes the cell phone address is different from the first message he received from the client.