The episode began with Yoshinori hiring Kogoro Mouri to come to a party he and his wife were hosting, as Misaki had been receiving ominous calls and gifts from an apparent stalker. After Kogoro arrived at the house with his daughter Ran and Conan Edogawa, Misaki was attacked in her room by an unidentified man. Soon afterwards, Conan found a photo of Misaki with Gerard Tenma, a French music composer that Hideki had hired to the company.
This led to Misaki revealing to her angered husband that she was previously in a relationship with Gerard in Hawaii (back when he went by his real name Junya), but that he had disappeared ten years prior. Later on, though, it was revealed that Misaki had been with Gerard at the same time as Yoshinori, as the aforementioned photo had been taken two weeks prior to their marriage. Enraged by Misaki's betrayal, Gerard wrote a song entitled "Red Nocturne", with the lyrics mentioning a pattern of flower types which were considered representations of betrayal and hatred. Feeling her new life with Yoshinori was threatened by Gerard, Misaki asked her lover to meet her at a cliff, where she shoved Gerard into the ocean.
Ten years later, after learning that Gerard had survived her attempt on his life and was making connections within her husband's company, Misaki began plotting to kill Gerard to prevent him from exposing her secret. Misaki began her plan by sending the ominous threats to herself, and additionally used a Beethoven statue and fishing line to set up the attack on herself. Afterwards, the evil Misaki set up another fishing line trap to murder Gerard, stringing a sword up inside the chandelier of the piano room and weighing the rope down with a tuning fork on the floor. Misaki then encouraged Gerard to play his song for them, resulting in Gerard being fatally impaled by the sword when he picked up the tuning fork.
Having set up for her past relationship with Gerard to be revealed, Yoshinori was believed to be Gerard's murderer and inspector Juzo Megure was prepared to arrest him. But Conan, having seen marks on the tuning fork and balcony from Misaki's fishing line tricks, deduced Misaki's villainous secrets and knocked out Kogoro to impersonate him and reveal the truth. When Misaki tried to argue that "Kogoro" had no proof, Conan revealed the final piece of evidence: wine left on the piano, having been left there by Misaki from having had wine spilled on her by Kogoro. At that, Misaki confessed to killing Gerard and setting up Yoshinori, justifying the frame job by claiming she had done so to protect their company (fearing that Yoshinori's apprentice, Masayo Tokudaji, was trying to seduce the company from him). After revealing how Gerard had written his famous song based on her betrayal, Michel Anglade (Gerard's manager) revealed that Gerard had recently changed the song out of guilt for driving Misaki to her crimes, causing the villainess to break down in tears. Misaki was then arrested (off-screen).
- Kayoko Fujii previously voiced blackmailer Kazumi Tatsumi and greedy murderess Kimie Hayase, villainesses who appeared in Season 2 and 3 of Case Closed, respectively.