Ross returns from fighting for Britain in the American Revolution to his native Cornwall only to find his ex-fiance, Elizabeth, now engaged to his cousin Francis.

Verity, Ross' cousin, is considered by everyone to be an old maid. They are all astonished when she attracts the attention of Captain Blamey at a ball. Unfortunately her father strongly disapproves of the match because the Captain is an ex-prisoner and former alcoholic. He forbids them to meet but Ross and Demelza take pity on Verity and encourage them to meet secretly so that Verity can get to know him better. Verity also tells Ross that Demelza is in love with him which amazes him. He still has feelings for the exquisite Elizabeth but he feels a growing affection for Demelza.

Ross' former employee, Jim Carter, stands trial for poaching and Ross gives evidence in his defence. Demelza, taken in as a maid by Ross, falls in love with him but learns that Ross still loves Elizabeth. She seduces him and becomes pregnant, running away because she knows that he isn't likely to want the child.

Ross learns that Demelza is pregnant and goes looking for her. Demelza gets into terrible trouble with her Puritan father and step-mother who can't stand the scandal. Before this Elizabeth finally agreed to run away with Ross and leave Francis whom she doesn't love.

Ross decides to marry Demelza because she is pregnant to Elizabeth's great displeasure. Ross'daughter Julia is born and he holds a party to celebrate. Elizabeth is very unhappy and not nice to Demelza.