Takagi and Sato are on a date at the amusement park. Meanwhile, Shiratori along with several officers are at the amusement park investigating a rumored drug deal involving a dealer in hiding named Asakichi Yakura; At the same time, they intentionally interfere with Takagi's date. Shiratori has one of the officers bring the Detective Boys to the park and puts them in Takagi and Sato's care. Takagi meanwhile plans to present Sato with a ring inside his green backpack and discovers a bag of heroin inside; He realizes he picked up the wrong backpack during the roller coaster ride. They return to the ride and learn from the attendant that no one returned asking for the backpack. Conan discerns the bag's owner was delivering the drugs without knowing what was inside causing Sato to suspect Yakura's involvement. The backpack's strap reveals the owner wears it on his left shoulder suggesting he is left handed, and proceeds to a photo-booth to examine the passengers with them on the roller coaster. The officers meanwhile misunderstand Sato's conversation, believing Kekkon (???, lit. Bloodstain) to mean Kekkon (???, lit. Marriage) and Heroin to mean Hir?en (????, lit. Reception) and causing them to believe Takagi proposed and allures them to seek out Takagi's backpack with the ring. At the photo booth, the four suspected are a golfer, a baseball player, soccer player, and swimmer. The golfer's writing reveals him to be left handed due to the ink smearing to the right.