As the battle wages on, we learn that a group of French soldiers just attacked the English camp, where they set fire to it and slaughtered all of the young boys (including the kid who used to be Falstaff's errand boy) who were left there to guard the equipment and supplies.
Fluellen and Gower declare this to be a cowardly act and say they're glad King Henry made the decision to slit the throats of all the French war prisoners.
Fluellen compares Henry to Alexander the Great, which is funny because Fluellen refers to him as "Alexander the pig." (Whoops. We think he meant to say "Alexander the Big.")
Gower argues that Henry is nothing like him because, unlike Alexander the Great, Henry "never killed any of his friends."
Fluellen reminds Gower that, actually, Henry banished his old friend, the "fat knight," whose name Fluellen has forgotten.
Gower helps him out. The name of the now dead "fat knight" is Sir John Falstaff. (The guy who died of a broken heart after Henry banished him.)
The scene cuts to King Henry, who is furious after learning that the young boys have been slaughtered at the camp.
Henry declares no mercy for the French soldiers who refuse to surrender and then repeats that he wants the throats of all the war prisoners slit open.
Montjoy (the French messenger) approaches and asks if the French can have permission to go onto the battlefield and sort their dead, since it wouldn't be right if the corpses of the mere commoners got to soak up any of the blood of the dead noblemen. (Hmm. Looks like the French soldiers don't consider themselves a "band of brothers.")
King Henry allows this but first, he makes Montjoy admit that the English have won the battle.
Fluellen and Henry reminisce about how the King's great uncle, Edward the Black Prince, once defeated the French nearby.
Fluellen reminds the King that he (Henry) was born in Wales (where Fluellen is from) and declares that he's proud to be Henry's countryman. (Go Britain!)
Williams shows up on the scene, and he's wearing the King's glove in his cap. (Remember, Henry and Williams exchanged gloves after getting into an argument.)
Henry spots the glove and decides it would be loads of fun to play a practical joke on Williams. (Looks like Hal the prankster is up to his old tricks, don't you think?)
Henry asks Williams about the glove in his cap and Williams replies that it belongs to a "rascal that swaggered with [him] last night." Williams promises that, when he sees the man, he's going to "take him a box o'th' ear." (Read: He's going to slap him upside his head.) He'll recognize the guy because he'll be wearing Williams' glove in his cap.
Henry sends Williams off on an errand and then gives Fluellen Williams' glove and asks him to wear it in his cap. Henry fibs and says the glove belonged to a Frenchman and, if anyone confronts Fluellen about the glove, it means that they're a traitor.