The battle has begun. Sir Walter Blunt, disguised as the King, encounters Douglas. Douglas assumes he is the King and tells him that he has earlier killed the Lord of Stafford, who was disguised as the King. They fight, and Douglas kills Blunt. Hotspur enters, and Douglas tells him the battle is over, for he has killed the King. But Hotspur informs him that the dead man was not the King, but Blunt. He tells Douglas that there are many men on the battlefield dressed as the King.
After they exit, Falstaff enters alone, cowering from the battle. Almost all of his hundred and fifty men have been killed, partly because Falstaff led them into harm's way, so he could draw the dead soldiers' pay.
The Prince enters and chides Falstaff for standing idly around. He asks to borrow Falstaff's sword. Falstaff claims that he needs a breather, having fought valiantly. He even claims to have killed Hotspur. Hal knows that Hotspur is still alive, and again asks for Falstaff's sword. Falstaff prefers to keep possession of his sword, but tells Hal he can take his pistol. Falstaff's pistol turns out to be a bottle of sack, and the Prince throws the bottle at him in disgust.
The Prince exits, leaving Falstaff alone. He says he would like to kill Hotspur, if he can, but he also realizes there is a good possibility that Hotspur will kill him instead. He plans to save his life if he can, but realizes the situation is not entirely in his control.
The historical battle at Shrewsbury took place in July, 1403. In the play, the fact that Henry IV has many soldiers dressed to look like the King visually suggests one of the issues in the play: the question of the legitimacy or otherwise of Henry as the English monarch. Douglas's confusion about who is the real King on the battlefield therefore has a wider significance.