This worthy knight was a man of parts; inasmuch as he was a soldier, a poet, and a gamester. At the time of his marriage he had passed his fiftieth year; moreover, he limped painfully and carried a crutch. His appearance, indeed, was far from imposing.

According to Aubrey, he was tall, had long legs, and was "incurvelting at his shoulders; his hair was but thin and flaxen, with a moist curl; his gait slow and rather as talking; his eye was a kind of light goose-grey, not big, but it had a strange piercingness, not as to shining and glory, but when he conversed he looked into your very thoughts." His personal defects, however, were to a great degree compensated for by his great wealth. Moreover he was surveyor-general of his majesty's works, had a town house in Scotland Yard, and a country residence at Waltham Cross in Essex. But there are some deficiencies for which wealth does not atone, as no doubt Lady Denham promptly discovered; for, before a year of her married life had passed, she renewed her intrigue with the Duke of York. His love for her seemed to have increased a thousandfold since fate had given her to the possession of another. At royal drawing-rooms he took her aside and talked to her "in the sight of all the world," and whenever she moved away from him he followed her like a dog.

Indeed, he made no effort to screen his passion, for not only did he make love to her in presence of the court, but he visited her at noonday, attended by his gentlemen, before all the town. Nor did Lady Denham desire to conceal the honour with which, she considered, this amour covered her, but openly declared she would "not be his mistress, as Mrs. Price, to go up and down the privy stairs, but will be owned publicly;" and in this respect she obtained her desire. Meanwhile Sir John was rendered miserable;and, indeed, his desperation soon overthrew his reason, and rendered him a lunatic. This affection first appeared during a journey he made to the famous free-stone quarries near Portland in Dorset. When he came within a mile of his destination, he suddenly turned back, and proceeded to Hounslow, where he demanded rents for lands he had disposed of years before; and then hastening to town sought out the king and informed him he was the Holy Ghost.

This madness lasted but a short time; and the first use he made of his recovered senses was to plot vengeance on his wife. Now there was one honour which she coveted above all others, that of being appointed a lady of the bedchamber to the Duchess of York.

This her royal lover, following the example of his majesty, sought to obtain for her; but the duchess, who had already suffered many indignities by reason of her husband's improprieties, refused him this request, which would render her liable to continual insult in her own court. The duke, however, had a strong will, and the duchess was on the point of yielding to his demand, when rumour announced that Lady Denham had been taken suddenly ill, and scandal declared she had been poisoned.

The wildest sensation followed. His royal highness, stricken with remorse and terror, hastened to Scotland Yard and sought his beloved mistress, who told him she believed herself poisoned, and felt she was now dying. The most eminent physicians were speedily summoned, but their skill proved of no avail, for she gradually became worse, and finally died, leaving instructions that her body should be opened after death, in order that search might be made for the fatal drug.

The surgeons followed these directions, as we learn from the Orrery state papers, but no trace of poison was discovered. For all that the public had no doubt her husband had destroyed her life, and Hamilton tells us the populace "had a design of tearing Sir John in pieces as soon as he should come abroad; but he shut himself up to bewail her death, until their fury was appeased by a magnificent funeral, at which he distributed four times more burnt wine than had ever been drunk at any burial in England."As for the duke, he was sorely troubled for her loss, and declared he should never have a public mistress again.