So what happens at Niagara Falls in Mary’s penultimate novel, Lodore? Not much. Because Lodore is not exactly prominent and/or pervasive in the publishing world these days, I’m going to offer you Mary’s entire paragraph—with a minor cut (nothing significant) indicated by the ellipses, which are mine, not Mary’s
One day … he stood watching that vast and celebrated cataract, whose everlasting and impetuous flow mirrored the dauntless but rash energy of his own soul. A vague desire of plunging into the whirl of waters agitated him. His existence appeared to be a blot in the creation; his hopes, and fears, and resolves, a worthless web of ill-assorted ideas, best swept away at once from the creation. Suddenly his eye caught the little figure of Fanny Derham, standing on a rock not far distant, her meaning eyes fixed on him. The thunder of the waters prevented speech; but as he drew near her, he saw that she had a paper in her hand. She held it out to him; a blush mantled over her usually pale countenance as he took it; and she sprung away up the rocky pathway.
Fanny Derham, 14, is the daughter of an old school friend; he encountered her in New York and agreed to accompany/chaperone her on her return to London. The paper in her hand is a letter from her father.
But … I want to focus on the Falls here. Note that Lodore feels that (quite common, it seems) urge to leap into the Niagara River and surrender to the power of the Falls. (I have actually felt it myself each time I’ve stood by that waterfall; however, I remain dry—and alive.)
In his story “The Imp of the Perverse” (1845) Edgar Poe talks about this compulsion at some length. He says because our reason violently deters it from the brink, therefore, do we the more impetuously approach it. Not surprisingly (this is Poe, after all!), the narrator is not considering a leap over/into a cataract but a murder, which he in fact commits, for which he escapes detection, until … read it yourself! (Link to story.)