Ross faces ruin as, along with the rest of his collective, he must sell to the Warleggans' company at a nominal price. At the same time the disease known as putrid throat sweeps through the county, claiming many lives and Dwight, still contrite over Keren, throws himself into trying to treat it. Elizabeth and her family are stricken and Demelza goes to help them but infects herself and her daughter with disastrous results. Divine justice appears to intervene as the Warleggans' ship and its cargo founder on the rocks and Ross leads the villagers in collecting its spoils from the beach. Demelza recovers from her sickness, only to face another setback to her marriage.

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.

Ross and Dwight stand trial for their part in the smuggling. A new tin lode gives Ross renewed hope in Wheal Grace, but it is George who is there for Elizabeth when her mother falls ill and deals Ross a bitter blow.

Aware of her husband's infidelity with Elizabeth Demelza does not hold back from expressing her disgust and defiantly attends a house party alone. Here she flirts with the amorous captain McNeil though loyalty to Ross causes her to draw the line at sex with him. Elizabeth's marriage to Warleggan finally goes ahead whilst Ross gets good news on the business front when repayment of a previous loan enables him to maintain the mine and a profitable find is made - one which will hopefully save his marriage.

Times are hard for the locals as grain is being sold to the highest bidders abroad. A corn riot breaks out in Truro, and the Carne boys, innocent bystanders, are among those arrested. MP George Warleggan manipulates the trial against them, but Ross does his best to save them, impressing Sir Francis Basset, who wants him to stand in the upcoming election. Demelza is torn between her admirer, Hugh Armitage and Ross, but she and Ross look to rebuild their marriage. Caroline has good news for Dwight, while Morwenna continues to endure life with her husband.

With Hugh's rapidly failing health eliminating him from standing in the election, his uncle, Lord Falmouth, thanks to Caroline and Demelza, joins with Sir Francis in agreeing that Ross should oppose Warleggan as the prospective member of parliament for the district. The result is a triumph for justice but Demelza must make an admission to Ross and, for her brothers, the path of true love continues to run anything but smoothly.

Ross is now member of parliament for Truro and making compassionate speeches opposing slavery and the use of child workers. Inevitably Warleggan, smarting from his defeat, links up with the disreputable Monk Adderley for revenge on Ross and a seat of his own whilst Whitworth seeks another way to discredit him. Returning to Cornwall, where Caroline has given birth to a daughter Sarah, Ross is called upon to save an ailing mine and also pays a visit to Elizabeth.

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.

Now suspicious about Valentine's paternity after Geoffrey Charles' observation, Warleggan is cold towards Elizabeth and, to force an early delivery of her unborn child to allay further suspicions about Ross being Valentine's father, she takes drastic measures - which do not end well. Drake, however, is overjoyed when Morwenna agrees to marry him whilst Lord Falmouth refuses to accept Ross's resignation from Parliament because of his duel with Monk Adderley.

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.

As George makes a lucrative alliance, the Poldarks are caught in a deadly web...

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.