Former Metropolitan Police Department (MPD) superintendent Tsutomu Muranaka, who is preparing to marry his fiancée Christine Richard, receives a dire death threat. In response, the police ensure his safety with protection measures as they practice defensive maneuvers to counter any potential threats during the wedding ceremony. Concurrently, police officer Yuya Kazami is on the trail of a serial bomber who has recently escaped custody when he is suddenly knocked unconscious. As Rei Furuya attempts to assist him, a bomb becomes attached to Yuya's neck, intensifying the urgency of the situation.
The following day, while visiting the MPD headquarters, Kogoro Mouri, Ran Mouri, Conan Edogawa, and the Detective Boys encounter a man with a tablet that unexpectedly explodes. In a heroic effort to protect Ai Haibara, [Megumi Hayashibara], Kogoro sustains injuries. Later, Conan meets with Rei and learns that this explosion may be connected to an earlier bombing incident that Rei and his colleagues—Hiromitsu Morofushi, Jinpei Matsuda, and Wataru Date—successfully thwarted years before.
As the story unfolds, Ran, Conan, and the Detective Boys travel to Shibuya to scout locations for the wedding, coinciding with the bustling Halloween festival. During this time, Christine receives a mysterious message instructing her to retrieve something, but with a meeting approaching with Muranaka, she has the Detective Boys deliver the package. Upon arrival, they discover a bomb similar to the one Rei defused three years prior and barely escape just before it detonates.
In another troubling turn of events, detective Chiba is abducted by an unknown assailant demanding to see Detective Matsuda, unaware that Matsuda has been deceased for three years. In a clever ruse, Detective Takagi disguises himself as Matsuda and meets with the captor, who unveils herself as Elenica Lavrentyeva, the leader of Nado Unichtozit, a group focused on capturing the bomber known as Plamya, responsible for Yuya’s predicament. Elenica reveals the tragic backstory involving her brother, who had been a hostage during the earlier bombing and was instrumental in evading the bomber’s grasp with Matsuda’s help, only to be killed outside MPD headquarters.
As tensions rise, police operatives infiltrate the Nado Unichtozit premises, but the group manages to escape. Despite contemplating canceling the wedding, Christine receives a threatening message compelling her to push forward. In an intimate ceremony away from the public eye, Muranaka and Christine exchange vows. Meanwhile, with Ran’s insightful assistance, Conan identifies a troubling pattern in the Shibuya road infrastructure linked to the paper held by Elenica's brother on the day he met his fate, leading him to suspect that Muranaka may be connected to Plamya.
In a shocking twist, Conan works alongside Nado Unichtozit to infiltrate the wedding, only for Christine to be unmasked as Plamya herself. She had manipulated the Detective Boys into locating a bomb-riddled building, orchestrated the arrival of Nado Unichtozit members in Japan, and rigged the entire Shibuya festival area with dangerous explosive compounds that could trigger a massive detonation if combined. As Christine attempts to escape in a helicopter, Rei arrives—having successfully defused the bomb attached to him with Yuya's help—and confronts her, engaging in a fierce battle that leads to the helicopter’s destruction.
In a dramatic conclusion, Muranaka subdues Christine, while Conan persuades Elenica to refrain from killing her. Working in unison, Conan, the Detective Boys, and Nado Unichtozit employ a massive inflatable ball to catch the two reactive liquids, thwarting the catastrophic explosion that would have devastated Shibuya. Christine is ultimately captured, the hazardous materials are cleared from the streets, and Muranaka assures Elenica that her quest for justice regarding her brother's death will be honored.
