There are many reasons why Hamlet's revenge plot is important to the development of the play; most are specific to the story-line. Hamlet is set upon revenge because of instructions from a ghost, which has taken his father's form. This ghost tells Hamlet, "Revenge his foul and most unnatural murder", asking him to make up for the murder of King Hamlet by killing the current king and King Hamlet's murderer, Claudius. Several developments occur after this instruction. Firstly, there is the considerable development of Hamlet feigning madness because he believes it is necessary to do so in order to gain revenge. Because of this, the plot changes to head in a totally different direction. As a direct consequence, Ophelia, or more accurately Hamlet's love for Ophelia, is sacrificed as Hamlet believes that it is more important to avenge his father's honour than it is to continue romantic liaisons with her. As a spin-off of this effect, Ophelia herself goes mad and in the end kills herself.
As Hamlet is desperate for revenge, he tells the audience of his plans in his soliloquies to them. This is most clearly illustrated in Hamlet's soliloquy in Act Two, Scene Two, in which he describes how he is going to observe his uncle throughout a play which is focused on a murder of the same design as that of his father. The quote, "For if the King like not the comedy, why, then, belike he likes it not, perdy" shows Hamlet's intention to discover the king's secrets.