A female corpse is found in a tower apartment. There is a wound to the head of the corpse and several days have passed since her death. They also find out that the woman is not a resident. After finding out the apartment is tied to scenario writer Minagawa and his wife Etsuko, Naoki begins to believe that the room was rented out to the victim while the two were on a trip. However, the room was locked from the inside and no key was found nearby.