Hitchcocks ''Maguffin''

A MacGuffin ( sometimes McGuffin or Maguffin) is a plot device that motivates the characters and advances the story but has little other relevance to the story.

''A plot element that catches the viewers' attention or drives the plot of a work fiction'' 

Quote '' We have a name in the studio,and we call it the ''MacGuffin'', It is the mechanical element that usually crops up in any story. In crook stories it is always the necklace and in spy stories it is always the papers.''