Falkland, Book 4‪.‬

As Falkland's servant had waited without to deliver the note to Emily, Mrs. St. John had observed him: her alarm and surprise only served to quicken her presence of mind. She intercepted Emily's answer under pretence of giving it herself to Falkland's servant. She read it, and her resolution was formed. After carefully resealing and delivering it to the servant, she went at once to Mr. Mandeville, and revealed Lady Emily's attachment to Falkland. In this act of treachery, she was solely instigated by her passions; and when Mandeville, roused from his wonted apathy to a paroxysm of indignation, thanked her again and again for the generosity of friendship which he imagined was all that actuated her communication, he dreamed not of the fierce and ungovernable jealousy which envied the very disgrace which her confession was intended to award.