This Japanese story begins with a 6-year-old boy interviewing to get into a private school. He’s been prepared for the testing by going to a "cram school." He lives in a city high-rise apartment with his workaholic, exacting father and doting mother. Life is full of rules and piano practice and high expectations. Then the parents receive a call informing them that blood tests have revealed there was a baby switch at the hospital, that the boy they’ve been raising isn’t their son. When they meet the other family, it is a contrast of lifestyles—they have two more children and run a chaotic, informal household. The father has an appliance repair shop that is attached to the home; he is fun-loving and present, but also unambitious and unconventional.

The hospital administrators want them to “switch back” before the boys start school, so there is a looming deadline. All the participants must take a look at themselves and what family means to them. One of the best parts of this film is you genuinely don’t know what should happen, what they should do to resolve this impossible situation. Can you just give up your child and adopt a stranger into your family? Should you keep a kid that isn’t yours, forsaking your own biological child? The film examines our assumptions about nature versus nurture, and heartrending questions come up about what it means to be a father, or a son, or a family.