About a family that lives on the outskirts of Seoul which consists of the father, his wife, their three daughters, and their one son. However, one day, a young man, who was a member of an idol group, shows up at the household claiming that he is the son of the family.
Kim Yeong-cheol as Byun Han-su/Lee Yoon-seok (60) — He is the owner of a Snack Bar and the father of the four kids. His identity was changed to Byun Han-soo after getting his identity switched with his best friend due to an accident. He was a former Judo player back in high school but ever since he was accused of a crime he didn’t do, he was forced to go to jail. After getting his identity switched, he was forced to keep his best friend’s name after his wife Young-shil got pregnant with Joon-young.
Kim Hae-sook as Na Young-sil (58) — The mother of the four kids and Lee Yoon-seok’s wife. She works along side with Yoon-seok at the Snack Bar while raising her four kids. She met Yoon-seok at a hospital while she was working as a nurse. She was the only one who stood beside Yoon-seok ever since he was released from jail since she was the only one who believed his story. She begs Yoon-seok to keep his name as Byun Han-soo after she got pregnant with Joon-young.
Ryu Soo-young as Cha Jeong-hwan (38)— The only child of Cha Gyu-taek and Oh Bok-nyeo. Even though he works as a PD at KBC studios, his show is losing popularity and since it is losing popularity, they decide to cancel his show. He was in a relationship with Hye-young while they were in college but broke up after his mother forced Hye-young to break up with him which caused him to find out why. He eventually gets back together with Hye-young after sleeping together and they eventually get married.
Min Jin-woong as Byun Joon-young/Lee Joon-young (35) — He is a 9th Grade Civil Servant and Lee Yoon-seok and Na Young-shil's oldest son and 1st child. He has been taking and studying his Civil Servant exam for almost 5 years and he eventually passes the test his 5th year. He has been dating Kim Yoo-joo while studying for his exam but after getting her pregnant by accident, they decide to get married.
Lee Yoo-ri as Byeon Hye-yeong/Lee Hye-yeong (34)—She is a lawyer and Lee Yoon-seok’s and Na Young-shil’s eldest daughter and 2nd child. She dated Cha Jung-hwan back in college but broke up after Jung-hwan’s mother forced her to break up with him. After sleeping with him from fighting, they decide to start dating again and they eventually get married. Her personality is known for acting pretty while she is working.
Jung So-min as Byeon Mi-yeong/Lee Mi-yeong (31) — She is Lee Yoon-seok and Na Young-shil’s 2nd daughter and the 3rd child of the family. She was a former Judo player but after injuring her shoulder, she became depressed which caused her to be overweight. After deciding to start her life again, she decides to lose weight and find a job. She eventually gets a job as an intern at Gabi Entertainment and later as Ahn Joong-hee’s manager. Although she gets a job at Gabi Entertainment, she is having a little trouble working there since a girl name Kim Yoo-joo who bullied her back in high school due to her weight, works there. After she finds out that Yoo-joo is dating and marrying her brother, she decides to accept her as her family since her brother loves her. She starts falling for Ahn Joong-hee which caused her to become like Joong-hee thinking that they are related.
Ryu Hwa-young as Byeon Ra-yeong/Lee Ra-yeong (27) — She is a yoga instructor and Lee Yoon-seok and Na Young-shil's youngest daughter and 4th child. She is always known for using her social media account constantly and is always the first one to find out her siblings’ dating secret. She meets Park Chul-soo when he gets a job as a soccer coach at the training center she works at. She at first thought he was gay after mistakening his twin brother as his boyfriend. She eventually starts to date him after he confesses to her.
Lee Joon as Ahn Joong-hee (36)— He is an idol-singer turned actor at Gabi Entertainment and the real Byun Han-soo’s son. He lived in the U.S before he moved to Korea to become a singer. Although he is an actor, he can’t really act well which never gives him a chance to do a mini series. When he believed that Lee Yoon-seok is Byun Han-soo, it caused him to move into his house with his family to know what it’s like living with his “father.” He later starts to fall for Mi-young which made him start to believe that he is crazy. After he finds out that Lee Yoon-seok is not his father, he starts to have a hard time not forgiving him because he has fallen in love with Mi-young.
Ahn Hyo-seop as Park Chul-soo — A former soccer player and a soccer coach at the training center. He comes from a chaebol but after refusing to work at the family business, he decides to run away and cut all financial ties with them which caused him to sleep at the night duty room at the training center. He eventually dates Ra-young after confessing his feelings to her.
Lee Mi-do as Kim Yoo-joo — She is Gabi Entertainment Art Team Leader and Joon-young's wife after he got her pregnant. She bullied Mi-young back in high school because she was jealous how Mi-young’s father treated her. Yoo-joo’s mother left her which caused her father to get remarried.
Park Hye-sook as Kim Mal-boon — Na Young-shil and Na Young-shik's mother.
Lee Jun-hyeok as Na Young-shik — Na Young-shil's younger brother and Lee Bo-mi’s husband. His family was doing well with business until his business partner stole all his money and ran away which caused his family to be bankrupt. His former business partner later comes back and gives half the money back and uses that money to open a pizza parlor after winning a pizza contest with his wife.
Jang So-yeon as Lee Bo-mi — Na Young-shik's wife. She tries to make a living by selling homemade dish rags after her husband’s business went bankrupt. After winning a pizza contest with her husband and getting pregnant with twins, she eventually opens the pizza parlor with her family.
Jung Joon-won as Na Min-ha — Na Young-shik abd Lee Bo-mi’s son. He is a straight A student who is always the top of his class. He gets invited to be enrolled at a Science and Technology High School but chooses not to due to tuition. After meeting a pretty math teacher from a different high school, he decides to go there instead.
Kang Seok-woo as Cha Kyoo-taek – Cha Jung-hwan's father and a retired journalist who never got a scope. Although he retired, he never cares for his wife Oh Bok-nyeo and only cares for his dog Chico.
Song Ok-sook as Oh Bok-nyeo – Cha Jung-hwan's mother and the owner of the building Lee Yoon-seok and his family lives in. She tries really hard to get her husband to pay attention to her no matter how hard she tries. She was really against the idea of Jung-hwan and Hye-young dating and she is against it more after getting into a fight with Na Young-shil.