In this scene, Hamlet actually meets with the ghost himself and the ghost speaks to tell Hamlet what is important for Hamlet and the audience to understand in order to make sense of the rest of the play. It is in this scene that Hamlet learns the plot that his uncle put together in order to steal the crown of Denmark from Hamlet’s father and perhaps also from Hamlet himself. The ghost tells him, “sleeping in my orchard, my custom always of the afternoon, upon my secure hour thy uncle stole with juice of cursed hebona in a vial, and in the porches of my ears did pour the leperous distilment, whose effect holds such an enmity with blood of man” (I, 5: 59-65). Although the ghost calls for revenge against the man who killed him, he tells Hamlet to let fate deal how it will with his mother.
Even though Hamlet immediately agrees to avenge his father and to bend his entire will to do it, he also finds it necessary to prove his uncle’s guilt independently of the words of the ghost. He provides some reason for this later in the play, suggesting that the ghost may be a malicious spirit from hell sent to tempt him into its fires, but the earliest clues for this possibility can also be found in this scene. This is first the result of the ghost’s description of how he spends his time, “I am … doomed for a certain term to walk the night, and for the day confined to fast in fires, till the foul crimes done in my days of nature are burnt and purged away” (I, 5: 10-13). Since Hamlet idolized his father, also revealed in this scene, it is difficult for him to believe that his father could deserve such a fate.