Bernardo and Marcellus want to show Horatio the ghost that they saw wandering the halls of the castle. They believe that the ghost resembles the appearance of the deceased king.
King Claudius announces his marriage to Queen Gertrude. He thinks it is an appropriate way to alleviate the pain from King Hamlet's passing. Prince Hamlet is still mourning his father, but King Claudius tells him to just get over it and move on, which angers Prince Hamlet.
Before Laertes leaves to France, he has a talk with his sister, Ophelia. He tells her to be aware of Hamlet's true intentions with her. Ophelia tells him that she will be mindful.
Prince Hamlet sees the ghost of his dead father. They have a long conversation about how King Hamlet was murdered Prince Hamlet's uncle, Claudius. The ghost of King Hamlet has come back to avenge his death. He needs the help of his son, and now more than ever, Hamlet is willing to help at whatever cost.
Claudius and Gertrude summon Rosencrantz and Guildenstern (two of Hamlet's closest friends), because they are worried about his erratic behavior. Polonius also goes to visit the queen and king about their son, because he is concerned that he has gone mad with love for his daughter, Ophelia.
Hamlet puts on a play with actors that have arrived to town. The play is a reenactment of what happened to his father. He wants to see how Claudius reacts to it. Sure enough, Claudius storms out because he is so frightened.