As the film opens, Gianni (Kim Rossi Stuart) prepares to meet for the first time the child he fathered 15 years earlier. The boy, Paolo (Andrea Rossi), was born with cerebral palsy and is of below average intelligence as well as being physically handicapped. Paolo's 19-year-old mother died when he was born, and Gianni could not bear to see the baby, or to have any subsequent contact with him. Paolo has been raised by his uncle, the dead woman's brother. Now Gianni, who lives in Milan with his wife and baby, prepares to take Paolo to a rehabilitation facility in Germany.

Paolo is trusting and does not question Gianni's long absence from his life. He manages to walk with the help of a cane, and tries to function as independently as he is physically capable of. When Gianni tries to feed him with a fork, Paolo responds by feeding Gianni instead. Many such small gestures that Paolo makes towards Gianni loosen Gianni's reserve, and each begins to respond to the other with affection.

In Germany, neither Gianni nor Paolo understand the language--in this they are equally disadvantaged. Gianni meets Nicole (Charlotte Rampling), mother to a teenage girl whose palsied speech impairment makes her unintelligible to anyone except Nicole. From the way that Gianni interacts with Paolo, Nicole senses that Gianni is Paolo's father, although Gianni at first denies it, claiming he is a friend of the family. When Gianni finally is truthful with Nicole, and worries about how Paolo will survive as an adult, she warns him that suffering is inevitable for the parent of an impaired child.

Gianni is horrified by the intensive physical therapy regimen to which Paolo is subjected in the German rehab facility, and removes the boy from therapy. He decides to bring Paolo home with him, but as they are driving back to Italy, Paolo "acts out" and Gianni realizes to his great sorrow that Paolo wishes to return to his uncle and live as he has for the first 15 years of his life. He has the keys to the house he grew up in and doesn't want to give them up.