Sentence:  Gerard returned safely to his native land, and in the fantastic spirit of the times, he approached his own castle disguised as a pilgrim, intending to himself and his <WSD>Chatelaine</WSD>, the delight of a romantic surprise. ... He accordingly repaired, in the silent hour of midnight, when the castle was wrapped in sleep, to the well-remembered chamber of the <WSD>Chatelaine</WSD>. She was not alone. A handsome young page supplied the place of her long-absent lord. In the excess of his rage, Gerard killed his wife on the spot, but reserved the page for a more lingering revenge. 
Meaning of the word marked with <WSD> tags:  The mistress of a castle or large household. (from mid 19th c.)