Murder Case: Lover Swap.

Yoshiko Konno went on a winter trip in a car driven by her fiance, Yoichi Itokawa, but got lost due to a blizzard and arrived at a mountain cottage in the depths of a grove. They decide to rent a room. After greeting several men and women sitting by the fireplace, they enter the bedroom. In the middle of the night, Yoshiko woke up and, hearing a woman's voice from the next room, left the room to see what was going on...