Spoilers follow for both parts, both present-day murders and the death two years earlier.
The Ranpo Mansion Murder Case (Part 1) and The Ranpo Mansion Murder Case (Part 2) are international episodes 1200-1201 (Japanese episodes 1142-1143). This anime-original two-part story reveals Nanako Imai as the killer of Mizobata and Okumoto. Oguruma separately admits killing Katsumine two years earlier.
The distinction between the two culprits is crucial. Nanako’s revenge grows out of the earlier death, but the present murders cannot simply be assigned to the man responsible for it. The decisive evidence is much smaller than that shared motive: candles, the handling of gloves and a trace transferred to Ayumi’s scarf.
A literary celebration becomes a crime scene
The story commemorates the 130th anniversary of Edogawa Ranpo’s birth and is scripted by Takahiro Okura. Conan’s own name connection with Ranpo makes a visit to the writer’s former home an especially fitting setting for the Detective Boys.
Their teacher accompanies them to the mansion, where Professor Goto and his assistant Okumoto show them the storehouse used as a library. The shelves of valuable books delight the visitors. A portrait of Ranpo is temporarily stored upstairs.
When a lighter falls from Okumoto’s pocket, Goto sharply warns him about fire. That moment establishes how dangerous any flame would be in a building filled with irreplaceable books. The later candlelit scene therefore violates a rule the story has already made impossible to overlook.
A missing wooden tag leads police to Professor Goto
Detectives Sato and Takagi arrive with news of a murder in a nearby park. An item left with the victim is linked to the mansion: one of the wooden tags Ranpo used when lending books is missing. The victim, Mizobata, belonged to a group of Ranpo enthusiasts who visited the storehouse the previous day.
Mizobata had argued with Goto over smoking and fire. Goto had also been drawn near the park around the relevant time, leaving him with a weak alibi. Police take him away for questioning. Those circumstances make him look naturally suspicious, but his removal is useful to the actual murderer.
At the university cafeteria, the Detective Boys meet other members of the group: Okumoto, Nanako, Rika and Oguruma. Their conversation brings up Katsumine, who died after falling into a river two years earlier. Repeated anonymous requests for a renewed investigation had challenged the original treatment of his death as an accident.
The open window reveals a second murder
Later, an unusual light comes from the storehouse through a window that is normally kept closed. Upstairs, Okumoto is found dead in a seated position in front of Ranpo’s portrait. Candles surround him, and marks on his hand draw Conan’s attention. Nanako, Rika and Oguruma have no clear alibis for the relevant interval.
The setting makes the discovery especially eerie: a place introduced through the excitement of seeing rare books is now illuminated by the very fire its guardian feared. The portrait and candles give the scene a staged appearance, but their role in the murder is practical as well as theatrical.
The candles perform three jobs
Nanako uses the wish to photograph Ranpo’s portrait by candlelight as a reason to bring Okumoto upstairs. His reference to lighting becomes meaningful in that photographic context. The candles first provide a plausible purpose for the meeting.
She then deliberately extinguishes a candle standing on the floor and asks him to relight it. Bending down lowers his head and lets her attack him from behind with a rope. The scene is arranged to control his posture rather than rely only on overcoming him from an equal standing position.
Okumoto habitually writes notes on the back of his hand. As he dies, he tries to leave a message identifying the attacker. Nanako moves a candle to burn away that writing, giving the flame a third purpose: destroying his final attempt to identify her.
Why the gloves and Ayumi’s scarf matter
Nanako’s fingerprints can be found elsewhere in the storehouse, but not on the candle moved to destroy the message. That difference points toward her using gloves specifically when handling the candle. Okumoto’s gloves have been rolled up neatly in a way that matches Nanako’s habits rather than his.
There is also material evidence beyond the neat arrangement. Moisturizer Okumoto used on his hands transfers through the gloves to Nanako. She tries to wash her hands, but she has already folded and handed back Ayumi’s scarf on the storehouse stairs. Traces of the moisturizer remain on the scarf.
That small act toward a child ties her to the gloves even after she tries to remove the trace from herself. The deduction moves from the staged scene, to an unusual handling habit, to a transfer that can survive her attempted cleanup. It is the mystery’s strongest chain of physical clues.
Two years of grief and two different crimes
Katsumine was Nanako’s boyfriend. She could not accept the explanation that someone who handled alcohol poorly had simply become drunk and fallen into the river. When repeated requests for investigation failed, she pursued the truth herself. Mizobata and Okumoto had been with him that night.
Oguruma’s jealousy of Katsumine’s literary promise led to the earlier killing. Katsumine’s work was attracting attention for a newcomer’s prize, and Oguruma also stole his work. Mizobata and Okumoto cooperated in what happened. Nanako kills those two and intends to make Oguruma bear the blame for all the deaths.
The first murder also serves her second crime. By arranging suspicion around Goto, she gets the protective professor removed from the mansion for questioning and creates an opportunity in the storehouse. The apparently separate park and library scenes are consecutive steps in the same plan.
A nighttime confrontation in the park threatens Rika when someone approaches with a rope. Nanako intervenes, and Oguruma is pressed over the old death. Conan does not let that confrontation settle the newer crimes: his candle, glove and scarf evidence instead exposes Nanako, who admits the two murders. Oguruma admits pushing Katsumine into the river.
The books she still wanted to protect
Nanako leaves the storehouse window open because she does not want the flames to spread to Ranpo’s books. That concern makes her revenge more painful to contemplate, not less criminal. She can still care about something her boyfriend loved while deliberately taking other lives.
The visit ends with the teacher waking after dozing in the reception room and discovering that she has missed the action. It is a welcome comic release, but the lasting impression comes from the books, the fire warning and the folded scarf: ordinary signs of care become inseparable from the proof of murder.
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