Having come back from their trip to Kitanosawa, the Detective Boys and Sonoko have brought souvenirs for Kobayashi and Makoto, respectively. However, it turns out that their presents were swapped, since they both looked the same. They return to Mouri's, where Heiji has come for a visit after hearing that Conan has got stuck in an avalanche. He begins to speculate how the presents were swapped, starting with the car spinning out of control, Haibara switching the presents when she was alone, or Agasa swapping them when he went back to the van during a break, or the moment Sonoko and Ayumi bumped into each other and dropped their presents onto the floor.

Source: Detective Conan World

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Parent story: Meitantei Conan
Prequel: Meitantei Conan: Chinmoku no Quarter