Sweyn Ulfsson, King of Denmark, carried out his promises to Ralph, and sent his son Cnut with Hakon Jarl to invade England; and they appeared on the east coast with a fleet of two hundred ships, and actually put into the Humber, though rather too late to serve the purposes of the ambitious earl. William, whether really frightened, or moved by the lust of power which was rapidly gaining upon him, and which clouded his later years with hate and misery, made the descent of the Danes a pretext for the worst crime of his reign--the judicial murder of Waltheof;--for it must be noted that, with this exception, his conduct to the English princes was generous and mild. When the son of Siward had carried to William the news of the plot in which he had taken part, the Conqueror had received him graciously, and had pardoned him freely for his own share of the mischief. But he kept him at his side, although he did not call him a prisoner; and, soon after landing in England, arrested him on a charge of complicity with the Danes, who had been his old comrades. William had that excuse for thinking him dangerous. Then came Judith's opportunity. She hated the husband she had been forced to marry for State purposes, and stood forth as his accuser, pouring her poison into the ears of her royal uncle. Unfortunately William listened, and cast the son of Siward into prison at Winchester, where he languished for months, while a mock trial was going on, which many hungry Normans, who wanted his estates, were determined should end to their liking. Ivo Taillebois, who had been one of Hereward's most venomous foes, and whose lands adjoined those of Waltheof, was amongst the most clamorous for his destruction; and the Primate Lanfranc his best advocate and almost sole friend, recognising perhaps that it was by his persuasion that Waltheof had been induced to place himself in the power of the Conqueror.