The film is about a magical pre-adolescent boy whose personality and naïveté have profound effects on the people in his town. A happily married couple, Cindy and Jim Green (Jennifer Garner and Joel Edgerton) can´t wait to start a family and lives dreaming of what her son. When, suddenly, the young Timothy appears at the door of his house during a stormy night, Cindy, Jim and the small town of Stanleyville discover that sometimes the unexpected can bring some of the best gifts of life, although these do not last forever. The
Greens are informed by doctors that they are unable to conceive.
Jim convinces Cindy to dream up their ideal child and write the child's characteristics and life events on slips of notepad paper.
The couple places the notes inside a wooden box and buries it in the backyard garden.
After a thunderstorm, which seemingly affects only their property, a ten-year-old arrives at their home claiming the Greens as his parents
The Greens also discover that Timothy has a startling feature: he has leaves growing on his legs.
Timothy begins to attend school, where he meets Joni Jerome, with whom he begins a friendly relationship. Timothy eventually reveals to Cindy and Jim that his time of existence is short and that he will eventually disappear.
The adoption counselor is shown pulling up to the Greens' house in a car with the little girl who is to become the Greens' daughter, Lily.