A successful lecturer facing single motherhood devises a fake romance with a marriage-averse doctor — but keeping up the act proves harder than it seems.

Oh Tae Shik, rather, Oh Kyeon Shik, who has been preparing to become a detective while working a different job, is a private establishment security guard who earns 880,000 won in Daechi Dong, Gangnam. Thanks to his dream of becoming a detective, he is like a bulldozer who does not know how to give up. He always watched CSI and Detective Columbo's movies, analyzing their traits and building his dream of becoming a great detective. He manages to pass the written test, but he doesn't meet the hearing baseline and fails. Then one day, coincidence happens and a fugitive on the run gets caught by Kyeon Shik when he throws a bottle of water he just bought at the runner. Kyeon Shik becomes a hero thanks to this.

High school student Lee Shi Kyung suddenly moves out to the countryside and transfers to a mysterious high school. Getting through unfamiliar experiences, he realizes the meaning of life and love.