Office worker Mayu takes the last train home after working late every night. One evening, a man catches a glimpse between her legs while she sleeps, and being watched turns her on so much that she masturbates at home. She eventually dares to remove her panties and finger herself in an empty train car. When the same man discovers her, they begin secretly masturbating together. Mayu finally beckons him over, makes him lick her pussy, and their strange relationship ends in discreet sex aboard the train.