She could not understand Percy.

This was one of those awful moments, which she had been destined to experience once or twice before, when the whole personality of her husband seemed to become shadowy before her, to slip, as it were, past her comprehension, leaving her indescribably lonely and wretched, trusting yet terrified.
She thought that long ere this he would have flung back every insult in his opponent's teeth; she did not know what inducements Chauvelin had held out in exchange for the infamous letter, what threats he had used.
That her own life and freedom were at stake, was, of course, evident, but she cared nothing for life, and he should know that certainly she would care still less if such a price had to be paid for it.
She longed to tell him all that was in her heart, longed to tell him how little she valued her life, how highly she prized his honour! but how could she, before this fiend who snarled and sneered in his anticipated triumph, and surely, surely Percy knew! And knowing all that, why did he not speak?
Why did he not tear that infamous paper from out that devil's hands and fling it in his face?
Yet, though her loving ear caught every intonation of her husband's voice, she could not detect the slightest harshness in his airy laugh; his tone was perfectly natural and he seemed to be, indeed, just as he appeared--vastly amused.
Then she thought that perhaps he would wish her to go now, that he felt desire to be alone with this man, who had outraged him in everything that he held most holy and most dear, his honour and his wife...

that perhaps, knowing that his own temper was no longer under control, he did not wish her to witness the rough and ready chastisement which he was intending to mete out to this dastardly intriguer.
Yes! that was it no doubt! Herein she could not be mistaken; she knew his fastidious notions of what was due and proper in the presence of a woman, and that even at a moment like this, he would wish the manners of London drawing-rooms to govern his every action.
Therefore she rose to go, and as she did so, once more tried to read the expression in his face...

to guess what was passing in his mind.
"Nay, Madam," he said, whilst he bowed gracefully before her, "I fear me this lengthy conversation hath somewhat fatigued you....

This merry jest 'twixt my engaging friend and myself should not have been prolonged so far into the night....