Affluent architects Ryota and his wife Midori face a terrible dilemma when they learn that their six-year-old son, Keita, was accidentally switched at birth and is not their biological child. In the wake of this revelation, Ryota's sense of fatherhood is shaken to the core as he witnesses both his wife's enduring devotion to Keita and his own conflicting feelings of nature versus nurture. Now his decision on which boy is truly his son will change...

Dwelling on his past glory as a prize-winning author, Ryota wastes the money he makes as a private detective on gambling and can barely pay child support. After the death of his father, his aging mother and beautiful ex-wife seem to be moving on with their lives. Renewing contact with his initially distrusting family, Ryota struggles to take back control of his existence and to find a lasting place in the life of his young son.

Fashioned as a tribute to his parents, the film depicts one day in the life of the Yokoyamas, gathered together for a celebratory ritual that only gradually makes itself clear. Rather than focus on big dramatic moments, Kore-eda relies on simple gestures and domestic routines (especially cooking) to evoke a family's entire life, its deep regrets and its daily joys.