Conan tries to figure out the phone number to the boss of the Black Organization. Mouri is invited by a granddaughter of a rich household to solve these mysterious accidents that happen whenever someone tries to play a Stradivarius for her grandfather on his birthday. Four incidents have happened on that day already and it is about to come up again. Later a fire occurs and a man is burned to death.

Conan figures out the object was the real Stradivarius that lured the grandmother to fall to her death. He reveals the culprit to be Kyousuke. Kyousuke reveals that the Stradivarius was originally from his family. One day, the Kyousuke's father was asked by his brother, Choichirou, to burrow the Stradivarius. He then attempts to to send back a replica to Kyousuke's father, but was found out. In an argument, Kyousuke's father falls down the stairs. Choichirou orders his family to not call the ambulance and to staged it as robbery. This is the cause of Kyousuke's father's death. As Kyousuke is taken away, Conan asks him the tune of a song from the cellphone numbers and finds out the Boss of the Black Organization's number is the song of "The Seven Children".