Francisco is a watchman, and Bernardo comes to take over. Marcellus and Horatio join them a little later. They try to convince Horatio that they've seen the ghost of the King, but he doesn't believe it.
The ghost appears and Horatio agrees that it looks like the king. The others convince Horatio to try to talk to it but the ghost doesn't answer.
The ghost disappears, and they decide to tell Hamlet, the king's son and Horatio's friend, about his father's ghost.