Conan and his friends go to a hotel pool where Nagami, daughter of the president of Oiso Finance, drowns to death. She had been wearing a diving tank and searching the pool for her lost necklace. Based on the crime scene, Inspector Megure believes it may have been an accident. However, the hotel bellboys claim the body in the pool suddenly appeared.

Kogoro is at Nichiuri TV Office, filming "Detective VS Weather Reporter" with Yasumi Sekine while Conan and Ran watch at the sidelines with Yukio Kodama, Takuya Yamaguchi, and Hiroko Shinohara. After the filming, Kogoro and Ran rest in a room while Conan goes to a vending machine to buy a bottle of oolong tea. As he picks up the bottle, he notices Yasumi and Yukio conversing secretly; after the small talk, they head out and split off. Then, Takuya hesitantly comes out of a room and follows Yasumi, and Conan follows him. Yasumi meets with Hiroko, who tells her the stage is good and ready. Hiroko asks her if she wanted to check the stage, but she said no because she trusted her.