On 6 December Louis captured Hertford Castle from the followers of the new king Henry. Fitzwalter naturally asked for the custody of a stronghold that had already been so long under his care. The French urged that a traitor to his own lord was not to be trusted, and Louis told him he must wait until the end of the war. Fitzwalter was too deeply pledged to Louis to join the deserters. He was sent from London on 30 April 1217 at the head of a strong French force to raise the siege of Mountsorrel in Leicestershire, now closely pressed by the Earl of Chester. On his way he rested at St Albans, where his hungry troops ate up all the supplies of the abbey, according to abbey chronicler Matthew Paris. He raised the siege of Mountsorrel and advanced to Lincoln. He was met by the regent, William Marshall, whose forces were now joined by the Earl of Chester with the army that had besieged Mountsorrel. Fitzwalter was anxious for an immediate battle.
