Ryosuke and Kyoko, who were asked by the phantom owner of the office to transport a cello, came to the food capital of Hong Kong with a boy named Kindaichi who was going to visit his father Kosuke, a trading company employee. Ryosuke and the others immediately visit the Holmes Agency in Hong Kong, where they find Seiya, who has disappeared from the Yokohama office. Ryosuke and the others were astonished to learn that Seiya had been cooperating with the Hong Kong police force using three people of the same age as themselves, Lau, Kelly, and Chan, who were all very active in the police force. Then Momo and Igarashi visit Seiya all the way from Japan and request his help in investigating an incident that occurred in Yokohama. The case is the murder of a freelance journalist named Hisashi Hayase, who was found dead on a pier in Yokohama.