While discussing Conan's journey to London and the case he had to solve there, Conan and Ai once again discuss Conan's reckless behavior in ingesting the anti-APTX 4869 meant for his return journey in order to reveal himself to Ran. An accidental comment makes the other Detective Boys suggest that they play hide and seek inside an abandoned building Genta knows. As they begin playing (with Conan once again prevailing with his detective skills), Genta hears a strange knocking that Conan deduces is emergency code 252 - a plea for rescue. While searching through the building, they encounter two men, apparently demolition workers, who claim that they made the knocking sound with hammers. But noticing three consumed sushi bento boxes nearby and catching them with a trick question about how the house is to be torn down, Conan deduces they are fakes and have are really holding someone hostage in the building somewhere.