In the play Hamlet, by William Shakespeare, there is a play within the play. The name of the play is "The Mousetrap," and it is written by Hamlet to serve a special purpose, beside providing entertainment for the King and Queen. The play is about a king, Gonzago, who is murdered by his nephew, Lucianus. After the king is dead, Lucianus marries the widowed queen, Baptista, who had promised Gonzago before he died that she would never marry again if he were to die. Hamlet wrote this play to serve a very special purpose. He had "heard that guilty creatures sitting at a play have been struck so to the soul that presently they have proclaimed their malefactions; for murder, though it have no tongue, will speak with most miraculous organ" (1092).
This gives Hamlet the idea to write the play so that he can prove that King Claudius did in fact murder his father, King Hamlet. So, during the play Hamlet has his friend, Horatio, watch the King closely to see what his reaction is to the play. This is to prove that either the ghost of King Hamlet is "a damned ghost" or that King Claudius is truly guilty of murder (1099). After the part in the play where Lucianus pours poison into Gonzago's ear, both Hamlet and Horatio observe that King Claudius is deeply disturbed by the scene to the point that he rises and calls for light; thus, proving that he is guilty of the crime. The play also causes Claudius to realize that someone knows about his ghastly deed. This marks a turning point in the play because now Hamlet knows, without a doubt, that Claudius murdered King Hamlet; therefore, he is certain that he needs to seek revenge.
In conclusion, the play within the play plays an important role in the plot of Hamlet. The play, "The Mousetrap," provides Hamlet with the evidence he needs to prove that King Claudius murdered his father, King Hamlet. It also makes Claudius aware that Hamlet knows his dark secret, thus marking a turning point in the play.