The story begins with the arrival of a stoic, mature girl named in Conan’s elementary school class. Initially appearing as just another transfer student, she surprises Conan by revealing her true identity after school: she is Shiho Miyano , a former scientist for the Black Organization code-named Sherry .

Haibara reveals that a floppy disk containing crucial data about the drug—and potentially a cure—might be hidden at the home of , a university teacher she once stayed with. Conan, sensing a chance to regain his true form, rushes with Haibara and Professor Agasa to the professor's house. The Murder Case

Upon arriving, they find Professor Hirota dead inside a locked room, surrounded by fallen books. The local police initially suspect a tragic accident or a robbery gone wrong. However, Conan’s keen observation skills reveal a much more calculated crime:

Conan deduces that the "locked" door was a trick involving a cassette tape and a heavy dictionary.

In the English dub of Detective Conan (Case Closed), is titled "The Girl from Black Organization and the University Professor Murder Case" . This pivotal episode marks the first appearance of Ai Haibara , a character who fundamentally changes the trajectory of the series . The Mysterious New Student

The episode concludes with a haunting moment: Haibara breaks down in tears, confronting Conan about why he couldn't save her sister, Akemi, despite his great detective skills. This emotional climax cements Haibara as a permanent, tragic ally in Conan's fight against the Black Organization.

While the murder is solved, the victory is hollow. In the chaos of the investigation, the floppy disk containing the drug data is accidentally formatted or lost, destroying Conan’s immediate hope for a cure.