Friend Sister: Jung Tae is living with his girlfriend Young Ji. His friend Min Ho ends up living with Jung Tae and despite the fact that Young Ji doesn't like this situation, Min Ho who is shameless soon gets used to living together. Then one day, another woman appears at home, Jung Tae's former lover and younger step-sister In Hye. Her appearance leaves Jung Tae in great confusion, followed by a sex scandal between four feisty men and women.