The earl of Northumberland and his son, Henry Percy, called "Hotspur," had performed great services for Henry IV., in establishing and maintaining him upon the throne. "At the outset of his reign their opposition would have been fatal to him; their adhesion ensured his victory. He had rewarded them with territory and high offices of trust, and they had by faithful services ever since increased their claims to gratitude and consideration. ... Both father and son were high-spirited, passionate, suspicious men, who entertained an exalted sense of their own services and could not endure the shadow of a slight. Up to this time [early in 1403] not a doubt had been cast on their fidelity. Northumberland was still the king's chief agent in Parliament, his most valued commander in the field, his Mattathias. It has been thought that Hotspur's grudge against the king began with the notion that the release of his brother-in-law, Edmund Mortimer [taken prisoner, the year before, by the Welsh], had been neglected by the king, or was caused by Henry's claim to deal with the prisoners taken at Homildon; the defenders of the Percies alleged that they had been deceived by Henry in the first instance, and only needed to be persuaded that Richard lived in order to desert the king. It is more probable that they suspected Henry's friendship, and were exasperated by his compulsory economies. ... Yet Henry seems to have conceived no suspicion. ... Northumberland and Hotspur were writing for increased forces [for the war with Scotland]. ... On the 10th of July Henry had reached Northamptonshire on his way northwards; on the 17th he heard that Hotspur with his uncle the earl of Worcester were in arms in Shropshire. They raised no cry of private wrongs, but proclaimed themselves the vindicators of national right: their object was to correct the evils of the administration, to enforce the employment of wise counsellors, and the proper expenditure of public money. ... The report ran like wildfire through the west that Richard was alive, and at Chester. Hotspur's army rose to 14,000 men, and not suspecting the strength and promptness of the king, he sat down with his uncle and his prisoner, the earl of Douglas, before Shrewsbury. Henry showed himself equal to the need. From Burton-on-Trent, where on July 17 he summoned the forces of the shires to join him, he marched into Shropshire, and offered to parley with the insurgents. The earl of Worcester went between the camps, but he was either an impolitic or a treacherous envoy, and the negotiations ended in mutual exasperation. On the 21st the battle of Shrewsbury was fought; Hotspur was slain; Worcester was taken and beheaded two days after. The old earl, who may or may not have been cognizant of his son's intentions from the first, was now marching to his succour.