A boy named Rintaro asks the Detective Boys to investigate on a strange man named Yuuji Kamekura. Rintaro explains that Yuuji appeared one day at his family restaurant claiming he owes Rintaro's grandfather a favor and would like to work at the restaurant. Yuuji soon after begins living with the family and helps them improve the restaurant to the point the family are constantly busy with the costumers. The Detective Boys investigate and all but Conan are convinced Yuuji is planning to dig a tunnel into a store to steal merchandise. The Detective Boys learn from a manager of a jewelry store that a robbery occurred five years ago and the thief was never caught. The Detective Boys deduce that Yuuji plans to dig up the jewels he buried five years ago from the robbery under the restaurant which was under construction five years ago. Conan denies the absurd deduction but gives in when Haibara tells him Yuuji is a very simple person unlike previous criminals. The Detective Boys manage to catch Yuuji digging up for jewels and call the police, convicting him of his robbery five years ago.