After nearly twenty years of marriage, Jung Da Jung and Hong Dae Young seem to have settled comfortably into their family life. As the proud parents of 18-year-old twins, the devoted couple has worked hard to build a happy home together. But what appears to be an ideal life from the outside is, in reality, anything but. Fed up with Dae Young’s constant nonsense, Da Jung is at the end of her rope. When Dae Young announces that he’s been fired, Da Jung completely gives up. Convinced that life would be better without her husband, Da Jung wastes no time and files for divorce. Shaken by his wife’s decision to leave him and utterly disappointed by where life has taken him, Dae Young takes stock of his life. It doesn’t take him long to see all the places where things went wrong, and soon he finds himself regretting absolutely everything about his life. The moment these thoughts of regret enter his mind, his body instantly transforms into that of an 18-year-old, while his 37-year-old mind remains intact. Suddenly given the chance to start his life over, Dae Young changes his name to Ko Woo Young and enrolls in his children’s school. Seeing life from a completely different perspective, Dae Young soon discovers that, even with his middle-aged brain, he still has a lot to learn.