Ross Poldark returns from fighting in the American Revolution to his native Cornwall, finding his fiancée Elizabeth Chynoweth about to marry his wealthy cousin Francis and his home in ruins after his father's death. Ross is a reluctant wedding guest, along with George Warleggan, nephew of a prosperous banker, and his uncle Charles proposes financing him to move to London. Ross, however, stays in Cornwall, rebuilding his home. Whilst at the local market he rescues the waif-like Demelza Carne and takes her home to work for him. Her bullying father arrives with his sons to reclaim her but Ross's tenants turn up to help him and fight them off.

On the eve of her husband's trial Demelza ignores Ray Penvenen's advice and approaches Judge Lister for mercy but her plan is scuppered by George Warleggan. Warleggan is convinced that Ross will be found guilty but Ross is an immensely popular defendant and despite the intervention of Demelza's father and Warleggan's paid prosecution witnesses his own excellent defence, aided by the testimony of the captain whose life he saved, Dwight and surprisingly Jud, leads to an acquittal. Dwight also attends Francis following his failed suicide bid after his belief that Elizabeth had an affair with Ross and gets closer to Caroline, who is not sorry when outsider Trevaunance's election as MP causes a riot. Warleggan however is still desperate to acquire Ross's mine by any means whilst Demelza and Ross consider having another baby.