TL;DR may contains spoilers : Hamlet sees his dead dad's ghost, pretends to go crazy with revenge, actually goes crazy with revenge debatable , and everyone dies. The ghost of the King of Denmark tells his son Hamlet to avenge his murder by killing the new king, Hamlet's uncle. Hamlet feigns madness, contemplates life and death, and seeks revenge.
His uncle, fearing for his life, also devises plots to kill Hamlet. The play ends with a duel, during which the King, Queen, Hamlet's opponent and Hamlet himself are all killed. Late at night, guards on the battlements of Denmark's Elsinore castle are met by Horatio, Prince Hamlet's friend from school. The guards describe a ghost they have seen that resembles Hamlet's father, the recently-deceased king. At that moment, the Ghost reappears, and the guards and Horatio decide to tell Hamlet.
Claudius, Hamlet's uncle, married Hamlet's recently-widowed mother, becoming the new King of Denmark. Hamlet continues to mourn for his father's death and laments his mother's lack of loyalty. When Hamlet hears of the Ghost from Horatio, he wants to see it for himself. Elsewhere, the royal attendant Polonius says farewell to his son Laertes, who is departing for France. Laertes warns his sister, Ophelia, away from Hamlet and thinking too much of his attentions towards her. The Ghost appears to Hamlet, claiming indeed to be the ghost of his father.
He tells Hamlet about how Claudius, the current King and Hamlet's uncle, murdered him, and Hamlet swears vengeance for his father. Hamlet decides to feign madness while he tests the truth of the Ghost's allegations always a good idea in such situations. According to his plan, Hamlet begins to act strangely.
He rejects Ophelia, while Claudius and Polonius, the royal attendant, spy on him. They had hoped to find the reason for Hamlet's sudden change in behaviour but could not. Claudius summons Guildenstern and Rosencrantz, old friends of Hamlet to find out what's got into him. Their arrival coincides with a group of travelling actors that Hamlet happens to know well. Hamlet writes a play which includes scenes that mimic the murder of Hamlet's father.
