Disguised as a travel agent, “Su-ji” is a government spy with six years’ experience who can’t reveal her career to her boyfriend “Jae-joon.” After she lies again, her boyfriend breaks up with her and leaves without notice, leaving her struggling alone with her sadness. Three years later, while chasing an industrial spy in disguise as a cleaning lady, she happens to run into Jae-joon. He’s become an international certified accountant, and seeing him throws her feelings into doubt. Jae-joon has become tired of his girlfriend’s constant and suspicious lies. In one phone call, he tells her he’s leaving Korea to study in Russia. Three years later, disguised as a distinguished international accountant, he enters the NIS (National Intelligence Service) as an agent in its overseas branch. He’s a newbie who got a late start, but he’s highly motivated and takes off on his first field mission, chasing a Russian crime organization, when he runs into Su-ji. It’s shocking to see her now as a hotel cleaning lady, but his affections for her are as strong as ever… Lying is part of the job, secrecy is the name of the game in "My Girlfriend is an Agent".
Park Yong Ha portrays man who once had it all. A scam ruined his family and his father's company went bankrupt because of him. He wants revenge against those who made his life a living hell. Park Si Yeon is his girlfriend who works diligently in order to help him repay his debts.
Lee Kang Joo is a single mother who was abandoned by her previous boyfriend, Yoo Ho Nam. Ho Nam forgot that Kang Joo was pregnant with his child and went abroad to study. When Ho Nam returns to Korea, he wants to pick up where he left off his relationship with Kang Joo. However, Kang Joo, is not as willing to start over with Ho Nam. Choi Seung Hun is the son of Jung Soo Hee who is Kang Joo's mentor and boss. He has been pursuing Kang Joo for a while and hits a roadblock when Kang Joo's ex returns.
Chun Ji Ae and Yang Bong Soon are high school classmates who did not have the best relationship with each other. Ji Ae was the most popular girl in school whereas Bong Soon was the girl that was always made fun of. Years later, their roles are reversed as Bong Soon's husband, Kang Joon Hyuk, is very successful whereas Ji Ae's husband, Ohn Dal Soo, is just an average company worker. Things get complicated when Dal Soo starts an extra-marital affair with his boss's wife, Eun So Hyuk. How will Ji Ae react to this?
Son Hyun Joo will portray a man who is the eldest of four sons and works hard to earn money to support his family. He is also a man who cannot forget his first love. His mother wants him to get married because he is already 38 years old.
Na Rim (Lee Young Yoo), who came from a wealthy household, lost her family in a car accident when she was nine. After the accident, she suffered from amnesia so her uncle hired Oh Dal Gun (Kim Myung Min), an ex-ganster,to recreate a similar household with parents, sister, brother, grandparents and uncle in hopes that she would regain her memory. In a hurry, Oh Dal Gun ended up hiring all sorts of odd ball characters to act as members of Na Rim's family. None got along at the start and hilarious situation arose when all members tried to cope in front of the little girl and also to protect her from the one who caused her family's accident. Eventually they started to behave like a real family and cared for each other, proving that blood relation is not as important as a caring heart.
A man named KIM jumps into the dark, quiet waters of the Han River. He wakes up and finds himself lying on covered with sand. It is then that he realized that he failed to kill himself and simply drifted to an unknown island in the river. In one of the riverside apartment buildings, there’s a girl who hasn’t ventured out of her room for years. One day, she catches sight of a man living alone on an island through her binoculars and becomes intrigued. Day after day, his lonely but seemingly contented life triggers her curiosity and compels her to step out of her room after so many years.