Conan and the Detective Boys are participating into a kite-flying competition when one of the contestants falls into the river.

Conan, Haibara, Agasa and the Detective Boys spend the weekend at a cottage with the three sisters who own it and the little sister's boyfriend. After dinner, the little sister realized she ran out of medicine and her boyfriend volunteers to walk through the storm to bring her more. Once the storm has ended, everyone decides to look for him since he was taking too long, and they find him dead on the snow.