Lizzie Eustace was the very beautiful, superficially clever and completely selfish daughter of an admiral who was no credit whatever to the British Navy. Her wiles were sufficient to induce the wealthy Sir Florian Eustace to marry her, but within a few months he was dead, leaving her possessed; of a life interest in the Scotch property, Portray Castle, and an income of £4,000. There was also a diamond necklace, valued at £10,000 which she claimed had been given to her earlier by Sir Florian. Mr.Camperdown, the Eustace family lawyer, asserted with much energy that the jewels were an heirloom and could not he disposed of in the casual manner described by Lizzie, but she refused to give them up.
After a few months of widowhood, she began to search for another husband. Her first choice was Frank Greystock, her cousin, an MP and a rising barrister. Although badly in need of money, he did not rise to her bait as he was engaged to Lucy Morris. Her second candidate was Lord Fawn, an undersecretary in the India Office, who thought that her income would compensate for the fact that he did not love her. He proposed and was accepted, but when he learned about the Eustace diamond scandal he tried to withdraw.
Returning to London from Portray Castle, her hotel room at Carlisle was entered and the safe in which she was known to carry the diamonds was stolen. When the police arrived she did not tell them that the jewels were still in her possession. Lord George Carruthers, whom she had thought might be the "Corsair of her Byronic dreams," and who was a member of her party, was suspected of being in league with the thieves. The Eustace diamonds became the talk of the town, the gossip concerning them even reaching the old Duke of Omnium. Frank Greystock believed Lizzie's story that the jewels had been stolen and defended her against those who proclaimed it to he a clever ruse to retain them. Soon after, there was a second robbery from her London house and this time the jewels finally disappeared, although Lizzie still pretended they had been taken at Carlisle. One of the thieves and the jeweler who had acted as fence were convicted and given prison terms. When Lord George learned the truth he threw Lizzie over, as did Lord Fawn. Frank Greystock had had enough of her and married Lucy, whom he had continued to love despite some philandering with Lizzie. She went back to Portray Castle and shortly after married Mr. Emilius, a reformed Jew who had become a popular preacher in London.
"...Disraeli did not consume much contemporary fiction.... But soon after the appearance of The Eustace Diamonds, meeting Trollope at Lord Stanhope's dinner-table, the great man said to our novelist, 'I have long known, Mr. Trollope, your churchmen and churchwomen; may I congratulate you on the same happy lightness of touch in the portrait of your new adventuress?" - Escott