The play’s the thing
Wherein I’ll catch the conscience of the king.

– William Shakespeare

Hamlet, Act 2, Scene 2. Hamlet wants to gather more evidence on whether Claudius is guilty of murdering his father, as the Ghost has claimed. So he uses theater to assess the truth and test the guilt of the King. He plans to stage a play about a similar murder and watch his uncle’s reaction to it. An example of dramatic irony, as Claudius, along with Rosencrantz and Guildenstern know nothing of Hamlet’s plan to confirm his suspicions about the King.