Marcellus and Barnardo had seen the ghost twice previously and due to Horatio's disbelief; Marcellus has convinced him to stand watch with them that night.  They believe that the ghost resembles the dead King Hamlet.  Around one o'clock, the ghost appears.  Horatio attempts to speak with it but the ghost will not answer and leaves.  As Marcellus, Horatio, and Barnardo begin to discuss how the late king conquered Fortinbras of Norway and seized his land, the ghost reappears.  Again, Horatio implores it to speak and again, it remains silent.  The cock crows and the ghost exits.  The three then decide that the best course of action is to inform the prince, Hamlet, of what they have seen.  They believe that the ghost will speak to the prince, as it appears to be his late father.

Claudius, the new king of Denmark, thanks his subjects for their support through the death of his brother Hamlet and marriage to Hamlet's wife.  He then sends his ambassadors, Cornelius and Voltemand, to prevent a threatened attack from Fortinbras in Norway, who seeks to avenge his father.  Claudius then turns to Laertes who has come to request permission to return to France.  Laertes' father, Polonius, gives his consent and so Claudius grants his request.  Next, the focus turns to Prince Hamlet.  Hamlet expresses extreme grief and is told by Claudius that his focus on his sorrow is both stubborn and unmanly.  Further, he denies Hamlet's desire to return to school in Wittenburg.  The Queen also voices her desire that Hamlet remain with them.  Hamlet consents to stay and is left alone.  In his solitude, Hamlet laments the death of his father and the remarriage of his mother in less than a month from that day.  Hamlet feels that the marriage between his mother and uncle is incestuous and that nothing good will come of their union.  Barnardo, Horatio, and Marcellus enter here and converse with the prince.  Horatio agrees that the marriage and funeral occurred in rapid succession.  He then tells Hamlet that he believes he has seen the ghost of the dead king.  The other two men corroborate his story.  They tell Hamlet that the form looked sorrowful, pale, and refused to speak.  Hamlet tells the three men to keep their vision a secret and plans to join them for the watch that night. 

Laertes says goodbye to his sister Ophelia and warns her not to trust Hamlet.  He tells her that Hamlet is fickle and soon his affections will turn from her.  She asks him not to tell her to live strictly if he intends to live self-indulgently.  He reassures her as their father Polonius enters.  Polonius sends his son off on his return to France.  Polonius then questions his daughter about the nature of her relationship with Hamlet.  Upon learning of his affection for her, Polonius repeats the warning of Laertes.  He tells her to have more respect for herself and not to continue the relationship.  Polonius further instructs Ophelia to refrain from further contact with the Prince. 

Hamlet joins Horatio and Marcellus for the watch while Claudius drinks the night away inside.  The ghost appears and beckons Hamlet to follow.  The other men try to convince the Prince not to go after the apparition for fear that it will lead him into danger.  Hamlet will not listen and departs with the ghost.  Horatio and Marcellus decide that they must follow.