Ayumi decides that on the Detective Boys camping trip, she will attempt address Ai Haibara by her first name and to call her "Ai-chan". During the camping trip, they run into four college students who offer them a ride in their campervan to the top mountain to watch the fireworks. While driving down the mountain, one of the four college students, Yasumi Shirafuji, is found on the road dead.
Accident?
Location:Mountains
Victim:Yasumi Shirafuji
Cause of death:Blunt-force trauma
Suspects:Reiji Fukuura, Haruka Tendo, and Takuto Meshiai
Evidence atop the mountain suggests Shirafuji lost control of her bike and accidentally went over the cliff. Conan reveals that there is a lack of blood on the cement raising the possibility it was a murder made to look like an accident and that the suspects are the three college students.
Part 2
After a thorough investigation, Conan finds out how the body was placed on the road and who the murderer is.
Conan impersonates Agasa's voice and reveals that Shirafuji's body was murdered and placed atop the van. The culprit used the sunroof to hold down Shirafuji's body and wrapped her body in a plastic covering to reduce friction. When the sunroof was released, Shirafuji's body fell backwards while the campervan was in motion which explains why they found the body on the way back. Conan then reveals the culprit to be the college student Haruka Tendo, evidenced by her change of clothes. Conan reveals that her she changed to a pair of similar jeans but the design was slightly different and that she threw away her other jean as it contains Shirafuji's blood. Tendo confesses and reveals that she was pretending to be rich and she found out her friends knew the truth yet only used their relationship for money. Yasuumi flippantly badmouths Haruka while Reiji out of desperate greed decides on letting Haruka continue giving money so that he can join a race derby and then terminate the relationship by the end of their graduation. Tendo thereby aimed to kill Shirafuji and frame Reiji for the murder should the accident theory be debunked.
The Detective Boys and Haibara (particularly Ayumi out of sadness that such a seemingly nice person could kill) criticize Tendo out of shame, saying that she should have known that money could have never gotten her real friends in the first place and that it was wrong for her to kill out of this reason alone. Tendo breaks down.
During the ride back, Haibara allows Ayumi to call her "Ai-chan" upon accepting their friendship.
