The titular Doctor Thorne lives in the village with his niece Mary. She is of a similar age to the Gresham children and since the doctor is well acquainted with squire Gresham, Mary spends a great deal of time at Greshamsbury Hall even though nothing is known of her background. "However, the mystery of Mary's birth is only a mystery to the numerous characters in the tale. It is one of Trollope's most insistent principles to take the reader into his confidence."