도대체 무슨 일이야?

Coffee shop owner Il Woo and nail artist An Na are in a happy romantic relationship. They keep their relationship in a secret because of their age difference. Also, So Ra who has a crush on Il Woo, gets jealous of An Na and she tries to tear them apart. One day An Na’s grandmother gives An Na a card, the card is to make her wish come true. After that day she turns into a 10 years old girl, Han Na. An Na’s wish “to become young” comes true! Il Woo tries to find An Na since she disappeared suddenly. Il Woo thinks Han Na as An Na’s daughter, he takes Han Na to his house to take care of her. On the other hand, Il Woo and An Na help An Na’s grandmother to find her first love.