Forced into international travel without proper documentation in "The Fist of Blue Sapphire," Shinichi Kudo operates in his child form as Conan Edogawa. Kaito Kid smuggles him into Singapore hidden inside luggage. Upon arrival, Kid confiscates Conan's signature glasses, wristwatch, and regular clothing, stripping him of his typical investigative tools. To maintain anonymity in this altered state, Conan adopts the alias "Arthur Hirai" when questioned by an unrecognizing Ran Mouri.

Kid simultaneously disguises himself as Shinichi Kudo to infiltrate events surrounding the legendary Blue Sapphire jewel. Confronting greater threats—including Singaporean detective and behavioral psychologist Leon Lowe and other antagonists seeking the sapphire for destructive purposes—forces Conan and his usual rival into an uneasy, extensive partnership, shifting their dynamic from adversarial to cooperative.

Navigating unfamiliar Singaporean environments like Marina Bay Sands and local food centers, Conan demonstrates adaptability. His physical appearance features a deliberately applied tan altering his usual complexion. The plot requires him to rely solely on intellectual deductions and improvisation rather than technological aids, particularly during the climax where he aids in preventing the destruction of Singaporean landmarks. Key supporting characters include Makoto Kyogoku, who enters a martial arts tournament where the sapphire serves as prize, and Ran Mouri, who remains unaware of Conan's true identity despite close interactions.

The narrative confirms continuity with prior character development, including Conan's sustained physical condition and unresolved romantic tension with Ran. The film concludes without restoring his original body, maintaining his child form while highlighting his deductive prowess and ethical commitment to preserving life.