1855: When Doctor Thorne’s penniless niece, Mary, is excluded from the wedding preparations of her childhood playmate, she probes her uncle for the truth of her birth.

Sir Roger becomes seriously ill, and Dr Thorne believes that he will die soon. The railway entrepreneur's son pays him a visit, and to the docotr's horror, takes a liking to Mary. Miss Dunstable urges Frank to follow what his heart tells him.

Frank and Mary plan their wedding, but Lady Arabella is still determined to stop them going ahead with the marriage. Sir Roger's son Louis struggles to cope with his new position in society.