David, a science fiction writer recently widowed whilst looking for an adoptee, is finely matched with socially awkward young Dennis, who believes he's from Mars, prefers to live in a cardboard box, wears a weight belt to prevent himself floating away and likes hanging upside down. David and Dennis begin the hard process of learning about each other, from Dennis' incessant photo-taking, his inclination to eat only Lucky Charms and his stealing, to David's continuing love of his wife, his penchant for baseball and his own struggles to be accepted by others.