Occasionally Swapping.

High school classmates So-ra and Ha-neul go to a pension with their boyfriends Sang-woo and Si-hoo. On the first night at the pension, So-ra's drunk boyfriend Sang-woo enters the wrong room and ends up having sex with Ha-neul. Meanwhile, So-ra, who fell asleep first, wakes up, looks for Sang-woo, and hears the sound of the two having sex. Losing her temper in her revenge, So-ra seduces Ha-neul's boyfriend Si-hoo, who is also drunk and asleep in living room, and has sex with him as well.