Conan finally stops being the smartest person in the room long enough to actually care about losing someone. The mystery takes a backseat to watching Ran face real danger on a military vessel, and the franchise's best emotional moments arrive when Conan has to choose between solving the case and protecting her. By the end, you understand why this matters more than any trick or spy reveal.

An Aegis destroyer holds public exercises in Maizuru Bay, where a suspicious foreign ship was recently sighted. Conan, Ran, Kogoro, Sonoko and the Detective Boys all have tickets to the event. During the operations, a crew member finds a lieutenant's severed left arm. Conan comes to suspect that a foreign spy, known as "X," has slipped aboard to steal classified information that would leave Japan's defenses exposed. With Ran in danger, Conan works with the police at sea while friends and allies investigate on the mainland, racing to unmask the spy. The film is a mystery adventure with comic touches, made with the cooperation of Japan's Ministry of Defense and Maritime Self-Defense Force.