Conan reveal to them that culprit is Rinpei Urushiya. Takagi lets it slip he and Sato have slept together. Rinpei reveals he is Taii old owner who had him for a year and a half while he was kitten who was stray. He gave to Teishi when his wife was suffering from a animal loss. After the case, soon Taii went around for a bit and ended up with Azusa.
Conan, Ran, and Sonoko head to a cabin in the woods with Masumi to meet some of her brother's old friends to solve a mystery. Along the way, they saw a woman dressed in all red hiding but vanished when seen. When Conan and co. arrive they meet the friends of Masumi's brother: Tamami Minegishi, Sumika Kawana, Masaie Hakuya, and Jinsuke Ninda. Ran mentions the woman in all red thinking she was apart of the friends' group, and everyone panics believing her the killer, the Red Woman- who got her name by killing her husband who was having an affair, soaking her coat in blood- who killed their friend Satoko in the nearby bog 15 years earlier; since then, strange things have happened at the villa, so Masumi was asked by her brother to investigate. Ran, Sonoko, and Sumika clean the dining area and find the bath prepared, and since they finished their chores they get ready to soak. Masumi and Conan accompany Jinsuke for groceries, and on their return find Masaie dead in the bath tub the girls were about to use full of floating tomatoes.
Conan and Masumi affirm their deductions and prove Sumika Kawana was the one who killed Masaie by bludgeoning him and hiding him in the tub. She used a bat and a fan to create the sounds of a vacuum to sound like Masaie was upstairs when he was already dead. Conan also shows that tomatoes don't float unless there is salt mixed in with the water. By adding more salt, she exposed the tomatoes and the body creating an alibi. Masumi also points out that she was the woman in red they saw on the way to the cabin as she handed Masumi the photos from earlier to investigate without hesitation while the other thought she was a boy. She killed Masaie because he had Satoko play the Red Woman for a prank, and she fell into the bog and died. But since she killed Masaie, who attacked her? The real Red Woman appears, but Yamato and Morofushi arrive and take her away. The woman who attacked Sumika was Shinobu Kagawa, the mistress of the man killed by the Red Woman, because Sumika was dressed as her. The mistress picked up the knife from the crime scene 15 years ago and had been searching the forest for the red woman, not knowing that she was dead. Conan also suggest that maybe Satoko ended in the bog, because she was attacked by the mistress who mistook her, as she was wearing red clothes, for the red woman, so the girl tried to escape but drowned instead. Conan later finds Masumi's phone and a young girl with Akai eyes is with her.
File 865 was accompanied by a special booklet with information about major characters and the Black organization that had not been revealed in the manga, an interview with Gosho, and images of the drawing process for the file.
