Only a month after the old King of Denmark dies, his queen remarries —to his own brother. Hamlet is not happy to have his uncle as his new step-father. On the political front, young go-getter Prince Fortinbras of Norway plans to invade Denmark.
A ghost shows up on the castle battlements, looking suspiciously like the recently deceased King. The ghost has a message for Hamlet: his father's death was no accident. Hamlet is supposed to exact revenge, which, when you're talking about the current King of Denmark and the husband of your mother, is quite the conflict. Meanwhile, Polonius tells Ophelia, Hamlet's girlfriend, to end whatever it is she's doing with Hamlet.
Revenge shouldn't be too complicated, if you actually get it done. But Hamlet doesn't get it done. All he manages to do is go crazy, which is complicated in its own right, but more so when you're not sure if he's faking it or not. And then there are some treacherous pseudo-friends (Rosencrantz and Guildenstern), and Ophelia is no longer talking to Hamlet, and finally there's some strange sort of lie-detecting play that Hamlet has devised, which is supposedly going to prove whether or not King Claudius is guilty of murdering the former King.
Complicated? We'll say.
We'll give you two choices here: the play-within-the-play, or Hamlet's confrontation with his mother is more central. One way of thinking about it is to see Hamlet's interaction with Gertrude as the play's emotional climax, while the play-within-the play is the plot's climax. After all, this is the point when Hamlet definitively knows that Claudius is guilty; it's also the first action Hamlet actually takes in the name of advancing his revenge. Yet the emotional boiling point of the play happens in the next scene, when Hamlet rails on Gertrude and stabs Polonius.
The suspense builds when we wonder if Hamlet is going to die on or after the trip to England. We feel more suspense as Claudius and Laertes plot our prince's death, suspense that only increases with every added back-up plan. Will Hamlet die from one of the umpteen poisoned objects?
Everyone whose name you know dies, except for Horatio. Talk about "casual slaughters" (5.2.366). After four acts of delay, everybody finally gets some revenge, all in about five minutes. In the not-so-friendly-after-all duel, Laertes manages to wound Hamlet with a poisoned sword, which Hamlet then uses to wound Laertes back. To clean up all the loose ends, Gertrude dies from poisoning and Hamlet kills Claudius.
Horatio, Hamlet's friend, is basically the only Equity actor left standing, so he gets to explain to Prince Fortinbras of Norway why there are dead bodies all over the floor. And, hey, since the throne's empty —Fortinbras will just help himself. Happy ending? Not for Hamlet. But it might be a good ending for Denmark, since Fortinbras is exactly the kind of get-up-and-goer that the kingdom needs.