The 9th annual Detective Conan film sails aboard a 100 million yen luxury cruise, the Saint Aphrodite, a vessel built by the Yashiro Group that echoes a tragedy from fifteen years past when a cruise named Yashiromaru sank at sea. On board, Conan Edogawa [Minami Takayama] and his friends are invited to join the voyage through Serena, setting a stage where wealth and mystery intertwine with long-buried secrets.
On the second day, the cruise is rocked by murder and disappearance. The CEO of the Yashiro Group is found dead in her cabin, and her father—the President of the group—is missing, seemingly thrown overboard by the same killer. At the welcoming party, Richard parades his deductions and singles out the ship’s sub-designer Minako Akiyoshi [Yoshiko Sakakibara] as the murderer. Yet Conan, calm and calculating, does not share the same conclusion.
A disciplined thread of investigations pulls Conan toward a different culprit: Kusaka, a scriptwriter who worked in collaboration with Akiyoshi on a project tied to the ship. Kusaka reveals a tangled backstory: the accident from fifteen years ago was a calculated plan to sink the ship and collect insurance, and his own father was murdered when he uncovered that the captain had been drugged and left to die. In a desperate bid to escape, Kusaka sets off bombs and flees by sea, pursued by the Detective Boys. The chase intensifies as additional explosives threaten everyone aboard, forcing a mass evacuation as passengers scramble to safety. Amid the chaos, Rachel hides, later returning to the fray only to discover a “gold medal” crafted from seashells the Detective Boys had made for her, a clue that glints with significance as the ship sways and she faints in the enclosed space.
In a dramatic turn, the truth arcs back to Minako Akiyoshi; she is revealed as the mastermind behind all three killings, and she admits that her father was the captain who died during the original sinking. Richard, whose rational instincts were initially misdirected, corrects his deductions and arrests Akiyoshi. His pursuit of truth had been tempered by a personal motive: he hoped to prove her innocence because of her striking resemblance to his late wife, but the deeper investigation exposes her guilt beyond doubt. As Richard and Conan begin to evacuate, they realize Rachel is missing; they ultimately locate her beneath the deck with the aid of a fire axe, a tense moment that underscores the peril aboard the swaying vessel. A helicopter finally arrives to lift them to safety, parting the crisis with a harrowing escape.
The post-credits scene ties the strands together in a quiet, character-driven beat. Conan explains how he knew where Rachel was—by interpreting a small clue: when he kicked a volleyball, Rachel heard a soccer ball, revealing she was in a space bordered by a tough wall. The Detective Kids reappear to share one final, tender gesture with Ran Mouri [Wakana Yamazaki]: they present a better, more enduring “gold medal” for her and place it on her, a symbolic moment of celebration amid the danger they endured together.
