Conan and Sonoko arrive at a dojo in Osaka where Kyogoku is training. Takami, the master of the dojo, once provided Kyogoku with a great deal of help with his karate training. While Conan and Sonoko watch the children practice, Kajiyoshi shows up to get Takami's signature on their agreement. Operating the dojo has become difficult to the point that Takami has taken out a loan, and he is considering selling the dojo. Later, an important black belt is stolen from the dojo's display case. When Kyogoku is suspected of stealing the belt, he challenges Takami to a fight. If he wins, the dojo will remain open, and if Takami wins, he'll return the belt...
Sonoko a le grand honneur de se rendre au dojo où s’entraîne Makotu, son amoureux. Cependant, elle ne veut pas y aller seule et Ran doit surveiller les autres enfants. Elle traîne donc de force Conan, ce qui n’est pas une mauvaise idée car le dojo aura besoin de tout l’intellect de Sonoko l’endormie pour résoudre le mystère de la ceinture noire volée.
Conan acompaña a Sonoko a visitar al siempre increíble Makoto-san al dojo de un antiguo sensei suyo. Mientras observan el entrenamiento, el valioso cinturón del sensei desaparece… ¿Quién será el culpable? ¿Por qué habrá desaparecido el cinturón?
Un anziano insegnante di karate ad Osaka afferma di voler andare in pensione e ripone la sua cintura in una teca di vetro. Tuttavia, l'obi sparisce. Sul posto ci sono Sonoko, Conan e Makoto.
Conan acompanya Sonoko a visitar el sempre increïble Makoto-san al dojo d'un antic seu. Mentre observen l'entrenament, el valuós cinturó del sensei desapareix... ¿Qui serà el culpable? Per què haurà desaparegut el cinturó?
