Due to a recent fad, Sakamoto Ryoma histories have become popular. Capitalizing on this, Jirokichi Suzuki's museum has set up a Ryoma exhibit. Jirokichi wanted to purchase a prize item of Ryoma's for the exhibit, a gun belt with a large ruby, from the current owners Shishihiko Tarumi and Masanosuke Hanamura. Not wanting to buy it before having it evaluating by his own appraiser, Jirokichi instead arranged a space at the exhibit for the owners to display the gunbelt in the meanwhile. Elsewhere, Sonoko tells Ran that Kaitou Kid has sent an advance notice that he will be at the exhibit to return some items that were stolen 20 years ago from Shishihiko Tarumi's Ryoma exhibit by the thief Phantom Lady: Ryoma's letter to his wife talking about the belt, a pistol Ryoma was carrying, and a sake cup with a bloodstain when Ryoma was assassinated. Inspector Ginzo Nakamori and Superintendent Shintaro Chaki discuss the best strategy to capture Kid: Lure Kid in to allow him to to return what was stolen, but then prevent him from leaving.

Conan, Ran, Sonoko and the Detective Boys are invited to an island for free diving lessons, but bad weather prevents them from doing so. While walking around the island, they stumble upon a shooting of a promotional video by washed up actor Yuya Miyasaka. While they watch, they see that Miyasaka physically harrases many of the crew members. It starts to rain soon after and every one comes back inside, but Miyasaka is found murdered later on.