Doctor Thomas Thorne is guardian to his beautiful but impecunious niece, Mary, whose parentage he has always kept secret. Mary falls in love with Frank Gresham, heir to the dwindling Greshamsbury estate, but when Frank proposes, his parents insist that he must marry for money to restore his family's fortunes. Frank is torn between his love for Mary and his sense of familial duty, whilst Doctor Thorne must decide whether to reveal the secret he has kept for so long.

In Doctor Thorne Trollope explores themes of money and society and the conflict between tradition and the need for change. Part of the 'Chronicles of Barsetshire' series on which Trollope's reputation primarily rests, it outsold all of his other novels during his lifetime.