What's the nature of being a parent and of being a child? David is a widower grieving for two years. He writes science fiction and was considered weird as a boy. He meets Dennis, a foster child who claims to be on a mission from Mars, stays in a large box all day, fears sunlight, and wears a belt of flashlight batteries so he won't float away. David takes the six-year-old home on a trial. His sister and his wife's best friend offer support, but the guys are basically alone to figure this out.