Set in Denmark, some time after the king's death, Prince Hamlet learns from 2 castle soldiers that the ghost of his father has just appeared to them. The ghost later appears to him & tells him that he was poisoned & murdered by his uncle, who has just taken the throne & married his mother.
Hamlet is suspicious about Claudius but isn't sure whether or not he actually committed the murder. When a theatre troupe comes, Hamlet tells them to act out "The Murder of Gonzago" to depict the poisoning of the king. Based on Claudius's reaction, he will determine whether or not he is guilty.