In Act II of Henry IV Part I there is a theme of lying displayed.  Not only is there lying about the robbery but there is also lying between Lady Percy and Hotspur and Prince Hal and the sheriff.
  First off in Act II sc ii a robbery takes place.  Falstaff with his company must fight off the robbers.  Prince Hal and Poins are in disguise waiting behind a bush for the right time to come out so they see what really happens.  In Act II sc iv Poins and Hal are questioning Falstaff about he robbery.  Falstaff says he fights off four men, and then seven men etc.  His numbers keep getting bigger and bigger.  Hal and Poins know he is lying because they were there but also because he kept changing the numbers.
  Second, in Act II sc iii Hotspur receives a letter from someone saying he can't join his group because it's too dangerous.  Hotspur gets very upset.  He mopes around and isn't himself.  His wife Lady Percy notices and asks him what's wrong.  He lies and tells her it's nothing.  He is keeping everything from her.  That's a different theme so I won't go into that.
  In Act II sc iv towards the end of the scene the sheriff comes to the inn to talk to Falstaff about the robbery.  Falstaff goes into a room toward the back and pretends like he's sleeping.  Prince Hal talks to the sheriff and tells him that Falstaff is not there and that he will see him tomorrow.  Prince Hal is lying to the sheriff.
  Now you can see why I wrote a theme analysis on lying.  In three out of the four scenes in this act someone is lying to someone else.  It's not a good thing to lie but it adds a twist to this play.