Conan, Ran, and Sonoko go to a tangerine farm located in a mountainous region within the prefecture in order to pick fruits. Farm manager Terauchi Tetsuji scolds Sokono for carelessly picking and damaging his tangerines. Conan and his friends are treated to a variety of tangerine-based dishes at the Terauchi family home. At the recommendation of Tetsuji's wife Nobuko, they head up to the top of the mountain to watch the sunset. Just as they're finished watching the sunset, they see Tetsuji riding the agricultural monorail up the mountain, but...

Haibara loses her phone strap of her favorite soccer player Higo on the train. Realizing the man who mistook her strap for his son's was most likely on his way to go digging for clams, Conan, Ayumi, Genta, Mitsuhiko, and Amuro go to the beach for the still not recovered Haibara in order to look for them. With Amuro's help, they learn the son's name. The Detective Boys successfully use the beach house's announcement system to find the son, but the man who's been watching Conan and his friends steals the strap as the father and son return it to them...