It is 1794, and Ross must traverse new family, new loves and new battles, as the French Revolution casts a shadow over life in Cornwall.
Ross and Demelza look to forget the past and rebuild their marriage, but new arrivals threaten their fragile reconciliation.
As Elizabeth becomes more ambivalent about Valentine, George courts Sir Francis Basset for the vacant magistracy position. Ross is reintroduced to Tholly Tregirls, an old friend of his father's and a ne'er-do-well who has returned to area. Verity returns to Trenwith, awaiting word from her husband, Andrew, whose ship is en route to Lisbon, while Elizabeth feels the sting of Morwenna and Geoffrey Charles's connection.
Ross is ordered to leave Roscoff under threat of execution. He travels with Tholly to meet his contact in France, but finds information about Dwight's fate comes at a high price. Sam leads a congregation of methodists in protest outside the church - only to face broken promises from George, who revokes their lease on the meeting house, which leads them to turn to Elizabeth for help. Geoffrey Charles has some words of advice for Drake, who has shared a moment of intimacy on the beach with Morwenna.
A grain ship grain is raided by starving villagers, and George arranges a harsh punishment for the desperate peasants while throwing a lavish Christmas party to impress the local gentry. Caroline hears news that the Admiralty has arranged for the release of the British officers, but Ross is not convinced. Demelza gives birth to a daughter, and warns Morwenna against a relationship with Drake.
The French Royalists plan an invasion, which Caroline hopes will lead to Dwight's release. However, Ross is convinced this will only make matters worse, and recruits a band of allies, including Tholly, Zacky, Drake and Henshawe, to help him free Dwight from prison. George schemes to further his political ambitions, and when he learns of Ross' plan, he uses it as a means to discredit his rival, accusing him of recklessness - a charge that may prove true when the rescue mission proves to have fatal consequences.
The Poldarks learn that their friend Dr Enys needs immediate care, suffering distress following his internment in France. In reaction to Ross' rescue of Hugh Armitage, George desperately needs to secure a connection to the nobility and so plans to force Morwenna's marriage to Osborne. Geoffrey Charles gives Drake his bible as a gift and naively reveals that Morwenna is to be wed. Drake confronts Morwenna and she agrees to marry him instead. Morwenna returns to Trenwith to tell George and Elizabeth that she will refuse Ossie's offer of marriage. Out of spite, George has Drake arrested for the theft of Geoffrey Charles' valuable bible, a crime for which Drake will hang.
George learns of a vacant seat in Parliament for a Member of Truro and decides to pursue it. Elizabeth and Agatha prepare for Agatha's 100th birthday party, to George's chagrin, and Caroline hosts a fake wedding reception to which the great and good are invited. Meanwhile, there is a new arrival at the Whitworth vicarage.
Ross is adamant George will lose in the election and determines to get a headstone made for Agatha's grave, something Trenwith has neglected. George, meanwhile, questions Dwight over Valentine's legitimacy and - paranoid and jealous - shuts himself to Elizabeth, as Rowella begins to seduce Osborne Whitworth and Demelza receives tokens of Hugh's affection. Sam continues to pine after Emma, as Dwight instructs Osborne to forego intercourse with Morwenna and Cary informs Lord Falmouth that the Warleggans will be opposing Falmouth in the election. Ross returns from his mine to discover Hugh Armitage at Nampara with Demelza - and this time Hugh's attention does not go unnoticed..