As the Poldarks look to rebuild their marriage and the Enyses to increase their family, Cornwall struggles under the Warleggans, whose power threatens all they hold dear.

The Poldarks determine to get their relationship on track and the Enyses announce they're expecting a baby. Hugh's worsening health threatens his chance to stand in the election, and the prospect of him remaining in Cornwall adds pressure to the Poldarks' fragile marriage. At the Sawle Feast, Tom Harry challenges Sam to a wrestling match. When Emma offers herself as the prize, Sam accepts.

Ross faces the challenge of Parliament and the Warleggans refuse to accept defeat. In Cornwall, Demelza contends with a failing mine and fixing Drake's broken heart. Dwight and Caroline welcome a baby daughter. Ossie meanwhile tends to a dying parishioner and George hosts an extravagant party at Trenwith.

Ross is reunited with his family at home, but tragedy strikes in Cornwall. Dwight tells Caroline some devastating news about Sarah. Ossie is seen visiting Rowella by her husband Arthur, who grows suspicious. Emma returns to give Sam her answer, whilst Drake is persuaded into courting Rosina.

George increases the strain on the struggling poor, driving Ross to make a risky gambit. The adversity the Poldarks face, however, may not be confined to Cornwall alone.

After it is revealed that Nathaniel Pearce embezzled Pascoe’s client’s funds, the Warleggans take action. In London, Ross finds Geoffrey Charles led astray by Adderley. Sam convinces Drake to return from exile following his abandonment of Rosina and Morwenna’s subsequent rejection and Morwenna reveals some news. Dwight meanwhile helps in the development of Truro’s infirmary.

Joining the Enyses and Ross in London Demelza enjoys the city life and accompanies Ross to a charity ball thrown by Warleggan to celebrate his wife's pregnancy. Here she attracts Adderley's predatory attention, leading him to challenge Ross to a duel, the outcome of which makes Warleggan even more anxious to crush Ross. Whilst Demelza, overwhelmed by events, returns to Cornwall, Morwenna has a message for Drake and Geoffrey Charles makes an observation.

Ross Poldark returns home after American Revolutionary War and rebuilds his life with a new business venture, making new enemies and finding a new love where he least expects it.