
The three traitors provide the play's clearest demonstration of Henry's transformed judgment before the French campaign even begins — his elaborate, theatrical exposure of their conspiracy establishes the same command of a room that will later win him a battle.
The Earl of Cambridge, Lord Scroop, and Sir Thomas Grey are three English noblemen who conspire with France to assassinate Henry before the fleet ever sails, a plot the king already knows of in full detail by the time the play stages its exposure at Southampton. Henry engineers an elaborate piece of theatre to reveal what he knows: he asks the three conspirators for their counsel on the appropriate punishment for a drunk soldier who railed against the king, and each of them argues eloquently for the harshest possible mercy-free justice, unknowingly condemning themselves before Henry produces the evidence of their own treason and hands each man his own commission papers to read.
Scroop's betrayal lands with particular weight — he had been, by every account within the scene, one of Henry's closest and most trusted companions, and the king's grief at this specific treachery is genuine and pointed, a wound closer to Brutus's betrayal of Caesar than a mere administrative crime. All three men, confronted with the proof, confess and accept their sentences with something like relief, grateful, they say, to have been stopped before the crime was completed.
Their execution is ordered on the spot, and the scene closes the play's opening movement with Henry's authority and perceptiveness fully established before a single Frenchman has been engaged — proof that the new king can detect and dismantle a conspiracy as decisively as he will soon conduct a war.
The three conspirators are motivated by French gold and, in Scroop's case particularly, a betrayal the play never fully explains, leaving the exact depth of his ingratitude toward a king who trusted him completely as one of its most unsettling loose threads.
The three men perform loyalty convincingly enough to nearly succeed, arguing for harsh justice against a minor offender in the very same breath that conceals their own far graver crime — and their swift, almost relieved confession once exposed suggests men who had perhaps already begun to buckle under the weight of a conspiracy they no longer had the stomach to complete.