Mrs. Foster’s trick is finally revealed: she heard the elevator get stuck and decided to leave her husband in there while she was away for six weeks, killing him. She behaves with the utmost propriety, calmly calling the elevator service. Her revenge, likewise, has been very intentional, but within the realms of propriety for her class status, because no one knows that she did it. She can be just as cruel and disloyal as her husband, it turns out, but she only chooses to do so in retaliation for his years of making her suffer.