Anthony Trollope 
The Eustace Diamonds 

The third novel in Anthony Trollope's Palliser series, The Eustace Diamonds bears all the hallmarks of his later works, blending dark cynicism with humor and a keen perception of human nature. Following the death of her husband, Sir Florian, beautiful Lizzie Eustace mysteriously comes into possession of a hugely expensive diamond necklace. She maintains it was a gift from her husband, but the Eustace lawyers insist she give it up, and while her cousin Frank takes her side, her new lover, Lord Fawn, declares that he will only marry her if the necklace is surrendered.