After nearly twenty years of marriage, Jung Da Jung and Hong Dae Young seem to be well settled in their domestic lives. The proud parents of a pair of eighteen year old twins, the devoted couple have worked hard to build a happy home together. But what seems like an ideal life on the outside is really anything but. Fed up with Dae Young’s incessant nonsense, Da Jung is at her wits’ end. When Dae Young announces that he’s been fired, Da Jung gives up completely. Convinced life would be better without her husband in it, Da Jung wastes no time in filing for divorce. Shaken by his wife’s decision to leave him and utterly disappointed in where life has taken him, Dae Young takes a hard look at 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 the thoughts of regret enter his head, his body is instantly transformed into that of an eighteen year old, while his thirty-seven year old mind remains intact. Suddenly given the chance to re-do his entire life, Dae Young changes his name to Ko Woo Young and enrolls himself in his children's’ school. Seeing life from an entirely different perspective, Dae Young soon finds that despite keeping his middle-aged brain, he still has a lot to learn.