On a cold night on the ramparts of Elsinore, the Danish royal castle, the sentries Bernardo and Marcellus discuss a ghost resembling the late King Hamlet which they have recently seen, and bring Prince Hamlet's friend Horatio as a witness.
After the ghost appears again, the three vow to tell Prince Hamlet what they have witnessed.
Denmark has a long-standing feud with neighbouring Norway, in which King Hamlet slew King Fortinbras of Norway in a battle some years ago.
Although Denmark defeated Norway and the Norwegian throne fell to King Fortinbras's infirm brother, Denmark fears that an invasion led by the dead Norwegian king's son, Prince Fortinbras, is imminent.
When Rosencrantz and Guildenstern arrive, Hamlet greets his "friends" warmly but quickly discerns that they are spies.
Hamlet becomes bitter, admitting that he is upset at his situation but refusing to give the true reason why, instead commenting on "what a piece of work" humanity is.
The protagonist of Hamlet is Prince Hamlet of Denmark, son of the recently deceased King Hamlet, and nephew of King Claudius, his father's brother and successor.
Claudius hastily married King Hamlet's widow, Gertrude, Hamlet's mother, and took the throne for himself.
That night on the rampart, the ghost appears to Hamlet, telling the prince that he was murdered by Claudius and demanding that Hamlet avenge him. The prince confides to Horatio and the sentries that from now on he plans to "put an antic disposition on", or act as though he has gone mad, and forces them to swear to keep his plans for revenge secret.
Privately, however, he remains uncertain of the ghost's reliability.