Coffee shop owner Il-woo and Nail artist Anna are in a happy romantic relationship. They keep their relationship in a secret because of their age difference. Also there is Sora, who has a crush on Il-woo gets jealous of Anna, she tries to tear them apart. One day, Anna’s grandmother gives Anna a card. The card is to make her wish come true. After that day, she turns into a 10 years old girl, Hannah. Anna’s wish “to become young” comes true! Il-Woo tries to find Anna since she disappeared suddenly. Il-Woo thinks Hannah as Anna’s daughter, he takes Hannah to his house to take care of her. So they start to live together… As some time passes, Il-Woo finds out Hannah was Anna herself and got surprised, but soon gets used to it. On the other hand, Il-Woo and Anna help Anna’s grandmother to find her first love. It is Granma's last wish to meet her first love. With their help, Anna’s grandmother finally meets her first love. Grandma tells Anna not to lose precious love, and she dies peacefully. By realizing the preciousness of love, Anna turns back into adult. Il-Woo and Anna finally meet again and realize how precious they are for each other and make a promise for everlasting love.

"Exactly What’s Going On" is a fantasy romance comedy about a 40 year-old woman who falls in love with a 25 year-old man, and ends up turning into a 10 year-old child.