Once Again follows the chaotic lives of the Song family, consisting of frugal father Song Young-dal and thrifty mother Jang Ok-boon, who have raised four adult children: Joon-sun, Gae-hee, Na-hee, and Da-hee. Despite their best efforts, all four children experience turbulent marital struggles, with three of them eventually moving back into their parents' family home as divorcees. As the parents and siblings navigate the social stigma, personal heartbreak, and daily comedies of living under one roof again, unexpected romances begin to bloom. Middle daughter Na-hee, a pediatrician, navigates a complex reconnection with her ex-husband and fellow doctor Gyu-jin, while youngest daughter Da-hee finds an unexpected bond with a former martial artist turned chef. Ultimately, the series explores the true meaning of family, forgiveness, and finding a second chance at happiness.