Hamlet Act III, Scene iv Summary

Inside Gertrude's room in the palace…
Polonius confers with Gertrude, advising her on the conversation she should have with Hamlet. He says she should tell Hamlet his pranks have gone too far, and that she has been covering his (Hamlet's) royal behind from getting into any real trouble.
With Gertrude's agreement, Polonius hides behind a curtain in her room to overhear her conversation with her son.
Gertrude reprimands Hamlet for upsetting Claudius with the play, but Hamlet turns the tables and starts attacking her for marrying her husband's brother. Hamlet grows so enraged that the Queen worries he will murder her – she cries out for help.
Polonius, still behind the curtain, hears Gertrude cry, "Help, ho!" Polonius also cries out, "What, ho, help!" While this does nothing to help Gertrude, it does alert Hamlet to the fact that someone is hiding behind the curtain.
Hamlet promptly stabs the curtain-veiled man, declaring he's found a rat. Polonius's utters his last words: "O, I am slain."
Gertrude asks, "What have you done?"
Hamlet admits he doesn't exactly know what he's done. He asks whether the curtain-spy was the King, and gets no reply from Gertrude.
Hamlet has no time to waste on the dead Polonius, and says this act was no worse than a certain someone else's choice to kill a king and marry his wife.
Gertrude gets in a tiff at the suggestion that she killed the King, but Hamlet is busy concerning himself with Polonius's dead body.
He says that he mistook the intruding old fool for a man higher up, though it did kind of serve Polonius right for being a busybody.
Note: Hamlet says he thought it was Claudius behind the screen but, we should point out that Hamlet just left Claudius (who was kneeling in prayer) before coming to Gertrude's room. How could Claudius have reached Gertrude's room so fast?
Leaving Polonius's dead body on the cold palace floor, Hamlet continues to attack his mother for her remarriage. He points out that his father was a convenient blend of all sorts of sexy beasts from Greek and Roman mythology, while Claudius is more like a mildewed ear of grain that infects everything around it.
Hamlet continues to berate his mother for switching from the very best to the very worst man, and wonders whether perhaps her senses have taken leave of her.
Hamlet's mom bends under her son's abuse, and says she now knows her soul is blackened by what she's done.
Hamlet gets increasingly mean and angry, and accusing his mom of being slick with the nasty sweat of a greasy bed. Then he finally spits out that her husband is a crown stealer and a murderer.
In the midst of these hysterics, the ghost appears to Hamlet once more.
Hamlet and the ghost have a little chat in which the ghost reminds Hamlet that he's got some revenge to attend to, and should probably get on that. After all, the ghost suggests, Gertrude's probably imagining the worst right now, as her insane son talks to her dead husband, who, as far as she can tell, isn't really there.
The ghost's entrance calms Hamlet, but as Gertrude cannot see her husband's spirit, she concludes that her son is insane.
(What's up with that? How come Hamlet's the only one who can see the ghost now? Has he totally lost it or, does the ghost choose to appear only to Hamlet?)
Hamlet immediately retorts that it shouldn't soothe Gertrude to dismiss his words as those of a madman, particularly when her deeds are still so foul.
Hamlet begs Gertrude to realize that her remarriage was a sin and she should stop having sex with Claudius.
Further, he makes a veiled threat against her, slipping in a conditional: "If you tell your husband that I'm only pretending to be crazy, your neck might break, which would be most unfortunate."
Hamlet then reminds his mother that he's been slated to leave for England with his "friends," Rosencrantz and Guildenstern, neither of whom he actually trusts. He says the little scheme Claudius is setting is fine, as he will basically be blown up by his own bomb. So Hamlet has more murder and mayhem up his sleeve.
Hamlet, lugging along Polonius's corpse, wishes his mother a good night.

Act IV, Scene i

Act III, Scene iii