In order to save her father from an accident, 26-years-old Kim Hye Ja uses a mysterious watch to rewind time in an attempt to prevent the accident, but fails. Desperate, she ends up rewinding the watch too many times and accidently aging herself, becoming a 70-years-old.
Confused and oblivious as to how she ended up like this, she sets on a journey to put everything back on track. Along the way, she encounters her family and friends who now do not recognize her, including Lee Joon Ha, a young man she loved, who yearns for her while struggling with his life.
When 70-years-old Kim Hye Ja and the young Lee Joon Ha come together to form an unlikely bond, a devastating and life-turning truth is revealed, the crux of all the time she lost.