Claudius explains to Laertes that he was powerless to act against Hamlet because the queen loves Hamlet her son, as do the public which is very forgiving of any wrong that Hamlet does. Claudius plumbs weather Laertes is given to revenge, and to what degree—”I’d cut his throat i’ t’ church”—before suggesting the plan of a fencing match between the two in which one of the blunt practice blades would actually be sharp.
Laertes agrees, saying that he has a poison that he will add to the blade to make sure. To which Claudius says he will make double sure by poisoning a drink that he will offer as a toast to him.
The queen enters and informs Laertes that Ophelia has drowned, by accident, but in which she did nothing to try to save herself.