A mysterious package comes in for Kogoro. Moments later, a diamond thief with a voice similar to Heiji's accidentally calls the Mouri Detective Agency asking for a ransom. Soon realizing that he has dialed the wrong number, the caller hangs up, but not before a familar voice says "Good morning!" on the other line. Conan deducts that the caller had meant to dial a similar number, and calls Heiji over to mimick his voice and call a list of similar numbers. Only one person responds; Iwatsume. The detectives approach him and question him to discover that the man had paid 10,000,000 yen to retrieve his stolen jewel. After realizing the meager ransom, which was a tenth of the value of the diamond, it is discovered that the returned gem was a fake.