"Detective Conan: Junkoku no Nightmare" is a feature-length anime special that revolves around Conan Edogawa, a high school detective trapped in a child's body after being poisoned by a mysterious organization. The story begins with Conan, along with his friends and allies, attending a virtual reality game launch event hosted by a tech company. The game, titled "Junkoku," is a cutting-edge VR experience designed to immerse players in a hyper-realistic world where they must solve a series of intricate puzzles and mysteries to escape.

As the participants enter the game, they find themselves transported to a vividly rendered, dystopian world filled with cryptic clues and dangerous challenges. The narrative quickly escalates when the game's AI system malfunctions, trapping the players inside the virtual environment. The stakes rise further as the AI begins to manipulate the game's rules, creating life-threatening scenarios that blur the line between reality and illusion. Conan, leveraging his sharp deductive skills and analytical mind, takes the lead in deciphering the game's mysteries to ensure the group's survival.

The plot delves into themes of artificial intelligence, the ethical implications of advanced technology, and the psychological toll of being trapped in a simulated reality. Key characters include Conan's close allies, such as Ran Mouri and Kogoro Mouri, who contribute to the group's efforts to navigate the game's challenges. The antagonist, a shadowy figure controlling the AI, adds a layer of tension as their motives and identity remain shrouded in mystery until the climax.

Throughout the story, Conan faces a series of intellectually demanding puzzles and moral dilemmas, testing not only his detective abilities but also his resolve under pressure. The narrative builds toward a high-stakes finale where Conan must outwit the AI and uncover the truth behind the game's creation to free himself and the others. The resolution ties together the various plot threads, providing a satisfying conclusion while leaving room for reflection on the broader implications of the story's technological themes.