At Southampton, Gloucester, Exeter and Westmoreland discuss the three traitors, whose plans are known to them and the King. Exeter has especially harsh words for Lord Scrope, who was a close confidant of the King.
The conspirators, unaware that their purposes are known, enter with King Henry. Henry asks them their opinion about the forthcoming military campaign. Do they not think that England's forces will accomplish what is necessary? Scrope says he has no doubt of it, if each man does his best. Cambridge chooses to flatter the King, saying that never was a King more feared and loved. Grey agrees, pointing out that Henry has unified the country, and old enemies of his father are now reconciled to the new King.
Henry then begins to set up the situation that will allow him to come down hard on the traitors. He tells Exeter to pardon a drunken man who had insulted him the day before. Scrope protests, saying that Henry is being too merciful. He calls for the man to be punished, lest leniency encourage more wrong-doers. Cambridge and Grey join in the call for punishment. But Henry replies that if they punish severely for small crimes, how will they be able to appropriately punish much larger ones? He sticks to his decision to pardon the man.
Then he hands them their commissions. They think that they are going to be empowered to act on the king's behalf in his absence, but their faces grow pale when they read the contents of the papers. Cambridge immediately confesses his guilt and begs for mercy, and Grey and Scrope follow his lead.
Henry refuses their request. He calls them monsters, because they were willing to betray their king for money from France. He mentions for the first time the plot itself, which was to kill Henry in Southampton. He reserves most of his wrath for Scrope, because they had been so close. He says it must have been the finest devil in hell who went to work on him to produce so great a betrayal. That devil may return to Tartarus (the hell of classical myth) and boast that he will never again win a soul as easily as he had Scrope's. Henry then lists all the qualities that it seemed as if Scrope possessed: dutiful, serious, learned, religious, of a noble family, steady in temperament, modest. And because Scrope has now proved false, in future, even the most excellent of men will be regarded with suspicion. Scrope's fall is so calamitous that it seems like another fall of man.
Henry orders Exeter to arrest the conspirators. Scrope repents, and begs for forgiveness, even though he knows he must die. Cambridge explains that it was not only French money that gave him the incentive to conspire against Henry. He had had the plot in mind earlier; the money merely made him act more quickly than he would otherwise have done. He thanks God for having intervened to foil his plot, and he asks for pardon.
Grey says he rejoices that his treason has been discovered. Like Scrope, he asks for forgiveness for his transgression, but he does not appeal against what he knows is the death sentence that has been passed on him.
Henry leaves mercy to God. He spells out their offenses in detail, along with what the consequences would have been had they succeeded. He says he does not want personal revenge, but he has to bear in mind the safety of the Kingdom, and so he delivers them to its laws, which means they must be put to death.
After the traitors are taken away, Henry turns his attention to France once more. He is confident, believing that since God has brought the treason to light, their course from then on will be a smooth one.
This scene shows that not only has Henry mastered the arts of diplomacy, he can also be ruthless when the situation demands it. He also shows considerable cunning in using the traitors' own words, when they speak about the need to punish offenders severely, against them. This makes Henry seem just rather than vengeful. It is as if the traitors have already acknowledged the appropriateness of the death sentence they are to receive.
It is also clear how far Henry has had to distance himself from his former carefree life. Not only has he rejected Falstaff, his tavern companion, but now he must condemn Scrope, one of his closest friends and confidants, to death. The demands of kingship are heavy. Henry has had to make himself hard, reining in his emotions in the cause of duty. He will be called upon to do the same thing again later, when Bardolph, another of his old companions, is condemned to death.