Swapping: Women's Fitness Trainer.

A sexless couple Eun-sook and Won-gil. Newlyweds Jong-beom and Na-jeong graduated from physical education. Jong-beom happens to be Eun-sook's personal health trainer and sex partner while working as a courier. Jong-beom introduces her wife Na-jeong as Won-gil's personal health trainer, and Won-gil receives sexual stimulation through Na-jeong. The two couples, who have been sleeping for a while, are boiling over and plan to have sex with each other...