In order to save her father from an accident, 26 year 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 accidentally ages herself, becoming a 70 year old.
Confused and oblivious as to how she ended up like this, she sets out on a journey to put everything back ontrack. Along the way, she encounters her family and friends who no longer recognize her, including Lee Joon Ha, a young man she loved, who yearns for her while struggling with his life.
When 70 year 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.
(Source: Nauriya at MyDramaList)