A Tangled Web by Lucy Maud Montgomery

Hugh Dark and Joscelyn Dark (née Penhallow) were sitting on opposite sides of the room, never looking at each other, and seeing and thinking of nothing but each other. And everybody looked at Joscelyn and wondered as they had wondered for ten years, what terrible secret lay behind her locked lips.

The affair of Hugh and Joscelyn was the mystery and tragedy of the clan--a mystery that no one had ever been able to solve, though not for lack of trying. Ten years before, Hugh Dark and Joscelyn Penhallow had been married after an eminently respectable and somewhat prolonged courtship. Joscelyn had not been too easily won. It was a match which pleased everybody, except Pauline Dark, who was mad about Hugh, and Mrs Conrad Dark, his mother, who had never liked Joscelyn's branch of the Penhallows.