The MacGuffin. Never more brilliantly explained than in this bit of dialogue from the thriller of tomorrow: Kiss Me Deadly.
The thing in question is a box that glows from the inside, that has been the quest of henchmen from the height of the Cold War right down to Pulp Fiction. When Velda Wickman utters these lines, the movie's already an hour gone and The Box has not yet made its appearance; our private-eye hero and his secretary are still unaware even of its existence.
"They." A wonderful word. And who are "they"? They are the nameless ones who kill people for the Great Whatsit. Does it exist? Who cares? Everyone everywhere is so involved in a fruitless search for what?
Did I forget to include a spoiler alert? Nah, you see, a McGuffin is nothing at all.