The Queen and Polonius come into the Queens Bed Chamber- Polonius tells the Queen to be straight forward with Hamlet (who is on his way) and "Tell him his pranks have been too broad to bear with, and that your grace hath screen'd and stood between. Much heat and him".
Hamlet is off set, calling for his mother. The Queen says she hears him coming and Polonius hides behind the arras (large wall tapestry).
Hamlet Comes into the Bed Chambers- Hamlet asks the Queen what's the matter. In return she does what Polonius' said to do, and tells Hamlet "thou hast thy father much offended". She means Claudius when she said this, not Hamlets father. Hamlet gets upset at that replies with "Mother, you have my father much offended". They exchange more angry words until:Hamlet: Come, come, and sit you down. You shall not budge. You go not till I set you up a glass (mirror), Where you may see the inmost part of you.
By this Hamlet is telling his mother to stay put; he's going to make her listen to the truth about herself, about all the things she doesn't want to see, about how he feels she is.
He scares with this, and she says "What wilt thou do? Thou wilt not murder me? Help, help, ho!"When the queen yells for help Polonius speaks from behind the arass. Hamlet responds to Polonius spying by "How now? A rat? Dead, for a ducat, dead!" and stabs the curtain, which kills Polonius.
After Polonius dies, the Queen asks Hamlet what he has done, and he responds by saying "Nay, I know not. / Is it the King?" He didn't know who he killed.
Hamlet moves the curtain to show his dead body. Hamlet says he thought Polonius was...