In medias res

A narrative work beginning in medias res (“into the middle of things”) opens in the midst of the plot. Often, exposition is bypassed and filled in gradually, through dialogue, flashbacks or description of past events. For example, Hamlet begins after the death of Hamlet’s father. Characters make reference to King Hamlet’s death without the plot’s first establishment of said fact. Since the play is about Hamlet and the revenge more so than the motivation, Shakespeare uses in medias res to bypass superfluous exposition. (Wikipedia)