Suk Jin, the eldest daughter of Seong Hak, a bank guard's five children, is always late for school because she manages the household in place of her deceased mother, earning her the nickname 'The Regular Latecomer.' Seong Hak hires a housekeeper named Ms. Choi, but she acts as a stepmother, mistreats the five children, sells off the household goods, and is then fired. Seong Hak remarries Ms. Gwa Cheon, who had run a stall in front of the company building for 10 years before being driven out and left with no means of livelihood. The kind Ms. Gwa Cheon diligently cares for Seong Hak's family, but she struggles to get close to the five children. Then, when the gold ring of the deceased mother, cherished by Suk Jin, goes missing, the family believes Ms. Gwa Cheon is responsible. Furthermore, when it's revealed that Ms. Gwa Cheon met her ex-husband, Seong Hak demands she leave the house. However, it is revealed that Jin Su lost the deceased mother's ring, and that Ms. Gwa Cheon made great efforts to help Eul Jun, who was being unjustly interrogated by the police. The five children then resolve their misunderstandings and call Ms. Gwa Cheon 'Mother.'