Loner Diane Ford (Michelle Monaghan) is a truck driver with an 11-year-old son, Peter (Jimmy Bennett), whom she never sees, and that's fine with her. But, when Peter's father, Len (Benjamin Bratt), falls ill, he asks Diane to take care of their son for a while. Eventually, Diane reluctantly agrees, but she quickly realizes that caring for a child interferes with her independent lifestyle -- and Peter isn't all that thrilled with the arrangement, either.