Marshall insists that he and Simon can stay up an extra hour because it's the night to set the clocks back--they have an extra hour. His Dad informs him that Indiana doesn't change their clocks and he and Simon, who is sleeping over, will have to go to bed. Marshall sets his watch back anyway, and when he wakes up he is in an alternate universe. A milkman saves him from evil garbagemen, and when he looks in the window in the back of the milk truck he can see his family and Simon at the breakfast table--in their universe Marshall is the missing kid on the back of the milk carton!
This is a cleverly written episode with special meaning to me because I live in Indiana. The first year I lived here I went through the same sorts of feelings Marshall did. Just recently, in the spring of 2006, Indiana changed their clocks for the first time since 1970.
Nikki Cox plays a girl that Marshall and Simon first see on the back of the milk carton. She had been missing for exactly one year. When Marshall enters the alternative universe he finds her living at the World of Stuff, and determines to save her, whether she likes it or not. I find it interesting, but not surprising, that someone can survive for a whole year at the World of Stuff.