Never did the fortunes of the second Henry appear more prosperous than at the very moment when the flight of his eldest son to the court of France, suddenly revealed the extent of the intrigues which were based upon the disaffection of his own children. Whilst the elder king was occupied in strengthening his defences upon the frontiers of France and in securing the important services of twenty thousand Reiters of Brabant, the younger Henry was busily corrupting the unfaithful adherents of his father, and lavishing grants upon the allies whose assistance he wished to purchase. The promise of Northumberland to William, and the offer of the fief of Cambridge to his brother, the Earl of Huntingdon, secured the active co-operation of both the Scottish princes;[400] and towards the close of summer, whilst the attention of the elder Henry was fully occupied in Normandy, the frontiers of England were suddenly invaded from the north. Siege was laid to Werk and Carlisle, whilst the main body of irregulars, according to the usual tactics of Scottish armies, was dispatched to lay waste the surrounding country. The Bishop of Durham appears to have secretly favoured the confederates, and the Scots were allowed a free passage through the lands of his diocese;[401] but their further progress was checked, before long, by tidings of the approach of a powerful force under the orders of Richard de Lucy, and Humphrey de Bohun, the Justiciary and Constable of England. Raising the siege of Carlisle, William retired across the borders, closely followed by de Lucy and de Bohun, who were beginning to retaliate upon the Lothians the ravages of the Scottish army in England, when the arrival of messengers from the south, brought the unwelcome intelligence of the landing of the Earl of Leicester on Michaelmas Day. Negotiations were hastily opened with the Scottish king, and so well did the English commanders succeed in concealing the real state of affairs, that they obtained a truce until the following January, and were thus enabled to lead back their army to oppose the Earl of Leicester, and to bend all their energies towards confronting the novel danger.[402]