'A dangerous cohabitation with the young sister-in-law begins!'
Won-jin is sent into a nearby region suddenly by the company. He is unprepared when he goes down so he calls his friend Chang-hoon who lives there. Chang-hoon lets Won-jin stay at his house for the time being but Won-jin gets to thinking.
The reason is, Chang-hoon's young wife Soo-yeong has a history with Won-jin. However, Won-jin decides to go to Chang-hoon's house to see Soo-yeong. Chang-hoon just happens to leave the house for a while and Won-jin meets Soo-yeong's glamorous friend Kyeong-hee who is also living there.
Won-jin starts living with Soo-yeong and Kyeong-hee who starts seducing him.