Ep. 622: Conan and Ai discuss his London trip while the Detective Boys investigate a mysterious knocking in an abandoned building.

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Conan and Ai revisit the incident where Conan took the APTX 4869 antidote to return to London and reveal himself to Ran. The Detective Boys decide to play hide and seek in an abandoned building known to Genta. During the game, Genta hears a strange knocking sound. Conan identifies this as emergency code 252, indicating a plea for rescue. The group investigates and finds two men claiming to be demolition workers who say they made the noise with hammers. Conan notices three empty sushi bento boxes nearby and uses a trick question to expose the men as impostors. He deduces that the workers are fake and that someone is being held hostage inside the building.