The final episode of St. Elsewhere revealed  MAR 11 2008

The final episode of St. Elsewhere revealed that all of the action of the show took place in the mind of an autistic child. Two detectives from Homicide: Life on the Street investigate a doctor from St. Elsewhere. Thus Homicide is a fiction. And so are 280 other shows that are connected to those two shows through crossovers and references. This page contains a map of all the crossovers, encompassing such disparate shows as Doctor Who, The King of Queens, and Leave It to Beaver. Wonderful.