When a smuggler is caught magistrate Francis cleverly ensures a lenient sentence but Ross suspects one of his miners, Nick Vigus, as an informer. Francis is also loyal to his cousin when they meet Warleggan at a party, where Elizabeth admits that she still has affection for Ross and Caroline jilts Trevaunance before Dwight reveals his feelings for her. Francis discovers copper in the mine but his jubilation is cruelly curtailed whilst Ross once more finds himself at the mercy of Warleggan, who has obtained his promissory note and has a financial hold over him.

A cheerless Christmas looms for the Poldarks with Francis drowned in the mine having only found fool's copper and Ross facing debtor's prison if he cannot pay Warleggan. Ross is also anxious to expose the traitor and agrees to a dangerous scheme to trap them whilst Demelza is troubled by his frequent visits to console Elizabeth - though Warleggan is quick to ingratiate himself with the widow. Ray Penvenen accuses Dwight of fortune hunting and tries to ban him from seeing Caroline but she is far too perceptive and realistic to give up the man she loves. She also bails out Ross, whose tenacity she admires, in his hour of need - whilst seeking to remain anonymous.

Ross joins a smuggling trip in the Isles of Scilly in order to meet Mark Daniel but, in his absence, George moves in on Elizabeth. Caroline convinces Dwight they must elope for a new life in Bath, and Captain McNeil plans to ambush the smugglers on their return.

In parliament Ross achieves some success on behalf of his constituents. He also meets Caroline, who has fled her recent tragedy and who introduces him to Monk Adderley. Back in Cornwall there is famine and sickness. However Morwenna and Drake are afforded a second chance when Whitworth's sins catch up with him although Drake, having broken off his wedding to Rosina Hoblyn, comes under suspicion.

Warleggan is triumphant to discover that the late Nathaniel Pearce embezzled money from Pascoe's, the bank used by Ross. With Ross in London - impressing prime minister Pitt - Demelza attempts to save the bank but fails and Warleggan takes full advantage to plot further. Drake is dissuaded from leaving the area by Sam but Morwenna still rejects him whilst Caroline returns from London with Ross for the opening of Dwight's new infirmary. Here Ross makes an impassioned speech which leads to the bank being saved. He also has a surprise for Demelza whilst Elizabeth has news of her own.

Ross and Demelza's domestic life is interrupted when a plea from Ross's old Army colonel compels him to London. Following Elizabeth's death, George's grief leads the Warleggans into uncharted territory.

Hanson's presence in Cornwall raises suspicion and as Demelza wrestles with how best to equip the community to look after itself, Morwenna lends herself to the cause and finds new hope. Geoffrey Charles and Cecily's relationship continues to blossom, but George's sanity continues to deteriorate and Cary struggles under mounting responsibilities. The Enyses look to challenge the county's high society by hosting a ball to introduce the Despards, before disaster strikes and Ross and Ned must spring into action together.

Ross tries to persuade the government to reinstate Ned as governor of Honduras, but Ned voices controversial views. The miners are distrusting of paper money. Morwenna visits John Conan. Demelza and Sam try to raise funds for a school.

Ned and Kitty face dire consequences and Ross attempts to help them. Cecily and Geoffrey Charles seek a life together against her father's wishes.

Demelza discovers the French are smuggling arms into Cornwall, but Ross is determined to take revenge on Merceron and Hanson for framing Ned and returns to London to confront them.