Question for Feb 24, 2010

X is a plot device that moves a story forward. Sometimes it is fundamental to the entire story itself. The specific nature of X is not important to the plot, as long as it serves as a motivation for characters to behave the way they do. X can be a tangible object that is desired by the characters, or it can even be something generic, or left open to the audience interpretation. Regardless, without X, the entire reason for the plot wouldn't exist. X (both, the name and the technique) was popularized by Alfred Hitchcock, who once stated that in crook stories, X is almost always the necklace, and in spy stories, the papers. One of the most famous examples of X are the letters of transit from the movie, Casablanca.

Identify X.