1855. Doctor Thorne's penniless niece, Mary, is devastated to learn that she is the illegitimate child of his late brother. Mary falls in love with the heir to the Greshamsbury Estate, Frank. Frank is under instructions to save his family from financial ruin by marrying money. Doctor Thorne acts as both physician and business advisor to a railway millionaire, who holds the fate of Greshamsbury.

It's Election Day, and Sir Roger Scatcherd wins the respect of the voters, but succumbs to ill health. Doctor Thorne does his best to ease the pain, but he senses the end is near. Scatcherd's son, Louis, is called for and he takes an immediate shine to Mary. Dr Thorne endeavours to embrace his new position as Louis' guardian, but is horrified to learn that he has romantic designs on his niece.

Frank plucks up the courage to propose to Mary and Dr Thorne gives him his blessing, but not before he has filled him in on the scandalous truth surrounding her birth. Lady Arabella continues her persecution of Mary, and is furious when Frank tells her he is set on marrying Dr Thorne's penniless niece. When Mary accepts, Louis vows to take his revenge upon the Greshams by seizing their estate.

While Frank and Mary plan their upcoming nuptials, Lady Arabella determines not to give up without a fight. She persuades Mary that marrying Frank would selfish, and if she truly loves him she should set him free. Meanwhile, Louis is struggling with his unpopular position in society and Mary's rejection. He takes great pleasure in insulting the Greshams when they invite him for dinner.