Jung Da-Jung (played by Kim Ha-Neul) is married to 37-year-old Hong Dae-Young (played by Yoon Sang-Hyun). They have have 18-year-old son and daughter. Jung Da-Jung works hard as a rookie announcer and she has a warm heart. She becomes completely fed up with her husband and is unable to deal with him anymore. Hong Dae-Young got fired from his job and he is looked down upon by his family. Jung Da-Jung hands him divorce papers.
Meanwhile, Hong Dae-Young looks at himself as an ordinary jobless middle-aged man. He regrets his life. At that moment, his body changes into that of an 18-year-old year old person, while his mind is still that of his 37-year-old self. Back in his teenage days, Hong Dae-Young (played by Lee Do-Hyun) was an excellent basketball player and also popular. Now, with his regained 18-year-old body, he changes his name to Ko Woo-Young and begins to live a new life.
During his new life, Woo-Young's goal is to get close to his children and become their good friend. Realizing that he has to pretend to be someone else to get close to those he loves, unable to take a good care of them, he realized what matters to him now. When Da-jung learns that Dae-young has another chance to get scouted for basketball by a prestigious college, she breaks things off for his own good. He begs her to let him stay, but Da-jung says that he already gave up his dream once for her and the kids, and this time she wants him to have a chance at a better future.
On the day of the finals game, Da-jung arrives at the school, but the thought of watching Dae-young play is too much so she turns to leave. She’s halfway across the bridge when Dae-young catches up to her, and Da-jung wails that he’ll regret this decision again. She thinks it’s her fault his life will be ruined again, and she wishes she’d never told him she knew who he was.
But Dae-young tells her, “It’s not your fault… it’s because of you.” He says that he used to think of giving up basketball as a sacrifice, but then he realized that those special moments with his family made him happier than basketball ever did. As he tells Da-jung this, she hears his voice change, and when she looks up, Dae-young is back in his older body. He continues that he didn’t realize how precious those moments were and would wish to go back eighteen years: “But Da-jung, you didn’t ruin my life. You gave me a chance. And my decision back then is the best decision I’ve ever made. I won’t miss out on that chance (again). You are my first love and my last. You are my life. I love you.”
They’ve learned some powerful lessons through their unusual experiences, and those lessons will carry them into the future with faith that if you cherish those you love, you will always have happiness.
Dae-young: Thinking back, endless happiness was always in our lives. It’s a common luxury all of us can have. For that happiness, we decided to love our decisions. We chose people based on love, and we are grateful for our decisions. As for my loved ones and myself… I would like to cheer them on to the end of time.
Da-jung: In life, even if you miss out on happiness, as long as you have that one person who will look for happiness with you, your life will be worth living.
Dae-young: Don’t forget that you love each other.
Da-jung: Be disappointed that you cannot cherish each other better.
Dae-young: And promise for a better tomorrow.
Da-jung: Like that, our lives will continue.
