Doctor Thorne is the third volume of The Barsetshire Chronicles by Anthony Trollope. The novel is set in Greshambury, unlike the first two volumes, set in the Cathedral town of Barchester. The readers come across Dr. Thorne and Mary, his niece living together. Mary is illegitimate, but Dr. Thorne raises her as his child to protect her reputation. Society treats illegitimate children as outcasts and isolates them from communal functions. Dr. Thorne reveals that Mary is a child of Sir Rodgers, a wealthy man using his last days drinking alcohol and living luxuriously. Dr. Thorne and Rodgers are close friends, but they both agree to keep Mary's identity a secret.
When Mary becomes a mature young woman, she falls in love with Frank, the son of Squire Gresham. In recent days, Gresham and his wife have had financial difficulties, and they believe that the only way to get out of this problem is by forcing Frank to marry a rich woman. Unfortunately, Mary is a poor woman who does not meet the qualifications set by Frank's parents. Frank's mother, Lady Arabella, asks him to dump Mary and look for a rich woman to marry.
The author shifts his attention to Sir Rodger Scatcherd's life. He continues to drink alcohol heavily despite the efforts of Dr. Thorne to help him curtail his drinking. Dr. Thorne and Sir Rodger are very close friends. Sir Rodger leaves his will to Dr. Thorne and instructs him to ensure his only son Philippe gets the inheritance after turning twenty-five years. A few years later, Sir Rodger dies of excessive drinking. Unfortunately, Philippe also becomes an alcoholic and dies before age 25. Sir Rodger's will states that if Philippe dies before inheriting his wealth; Mary becomes the sole heir.
Towards the end, Frank and Mary are unaware that she is about to become the richest woman in her town. Frank requests his father to bless his marriage with Mary, and at last, he does and blesses their union. Later, it is revealed that Mary is the sole heir to Sir Rodger's wealth. Everyone in Frank's family congratulates him for choosing to marry Mary.
