Asako Morishita is 40 years old, married for five years, and a housewife. She embarks on a journey to Ueno on a sleeper train. It is the first time for a married woman to ride a sleeper train, and also for her to be with a man other than her husband. The train departs with tension and anxiety. Exposing her naked body to a man for the first time in a long time, she writhes in shame and cries out in pleasure. A lustful affair between a married woman and a man unfolds behind closed doors as the train moves.