Hamlet stabs Polonius through the tapestry, thinking he has killed Claudius.
When he finds that he has merely killed a "rash, intruding fool," Hamlet returns to the business of "speaking daggers" to his mother.
Hamlet has been behaving in a most erratic and alarming way.
Claudius summons two of Hamlet's school friends, Rosencrantz and Guildenstern, in order to discover the meaning of this strange behavior.
Just as Gertrude appears convinced by Hamlet's excoriation, the ghost of Old Hamlet reappears and tells Hamlet not to behave so cruelly to his mother, and to remember to carry out revenge on Claudius.
Gertrude perceives her son discoursing with nothing but air and is completely convinced of his madness.
Though skeptical at first, Horatio sees the ghost and decides to report its appearance to Hamlet.
Meanwhile, a new king of Denmark has been crowned: Claudius, Old Hamlet's brother.
Horatio tells Hamlet of the appearance of the ghost and Hamlet determines to visit the spirit himself. Hamlet questions the ghost, who beckons Hamlet away from the others.
Meanwhile, the court adviser, Polonius, sends his son, Laertes, back to Paris, where he is living. When they are alone, the ghost reveals that Claudius murdered him in order to steal his crown and his wife.