The Eustace Diamonds

In this novel, the characters of Plantagenet Palliser, his wife Lady Glencora and their uncle the ailing Duke of Omnium are in the background. The plot centres on Lizzie Greystock, a fortune-hunter who ensnares the sickly, dissipated Sir Florian Eustace and is soon left a very wealthy widow and mother. While clever and beautiful, Lizzie has several character flaws; the greatest of these is an almost pathological delight in lying, even when it cannot benefit her. (Trollope comments that Lizzie sees lies as "more beautiful than the truth.") Before he dies, the disillusioned Sir Florian discovers all this, but does not think to change the generous terms of his will. Wikipedia