Henry invades France. Battle of Agincourt. Effect of the battle. He sailed for France in August 1415, with an army compact and well-equipped, but not very numerous. On the eve of his departure he detected and quelled a plot as wild and futile as that of Oldcastle. The conspirators were his cousin, Richard, earl of Cambridge, Lord Scrope, and Sir Thomas Grey, a kinsman of the Percies. They had planned to raise a rebellion in the name of the earl of March, in whose cause Wales and the North were to have been called to arms. But March himself refused to stir, and betrayed them to the king, who promptly beheaded them, and set sail five days later. He landed near the mouth of the Seine, and commenced his campaign by besieging and capturing Harfleur, which the Orleanists made no attempt to succour. But such a large number of his troops perished in the trenches by a pestilential disorder, that he found himself too weak to march on Paris, and took his way to Calais across Picardy, hoping, as it seems, to lure the French to battle by exposing his small army to attack. The plan was hazardous, for the Orleanists turned out in great numbers and almost cut him off in the marshes of the Somme. When he had struggled across them, and was half-way to Calais, the enemy beset him in the fields of Agincourt (Oct. 25, 1415). Here Henry vindicated his military reputation by winning a victory even more surprising than those of Creçy, and Poitiers, for he was outnumbered in an even greater proportion than the two Edwards had been in 1346 and 1356, and had to take the offensive instead of being attacked in a strong position. The heavily armoured French noblesse, embogged in miry meadows, proved helpless before the lightly equipped English archery. The slaughter in their ranks was terrible, and the young duke of Orleans, the head of the predominant faction of the moment, was taken prisoner with many great nobles. However, so exhausted was the victorious army that Henry merely led it back to Calais, without attempting anything more in this year. The sole tangible asset of the campaign was the possession of Harfleur, the gate of Normandy, a second Calais in its advantages when future invasions were taken in hand. The moral effects were more important. The Orleanist party was shaken in its power; the rival Burgundian faction became more inclined to commit itself to the English cause, and the terror of the English arms weighed heavily upon both. England and the council of Constance.