New series. The final series of the period drama begins. Ross travels to London to answer a plea for help from an old friend, and finds himself faced with a conspiracy masterminded by a slave trader - whose daughter has caught Geoffrey's eye. Demelza is confronted with a new enemy as she manages the family's affairs in Cornwall, while George remains devastated following Elizabeth's death, leaving Cary to take up the task of expanding a family empire that is driven into dangerous territory by grief.
George pursues the fruits of his new alliance, but his lingering grief has unexpected consequences, and as Ned confronts the man responsible for his downfall, Demelza fears they are entangled with forces beyond their control. Meanwhile, Drake and Morwenna continue tentative steps forward in their relationship, Geoffrey Charles learns he must tread carefully if he is to gain Cecily's father's favour, and Ross tries to find a man who may hold the key to clearing Ned's name, but finds himself in a compromising situation.
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 is given hope for the Despards' return to Honduras, but finds his new arch enemy Ralph Hanson has returned to Truro. Dwight gains unexpected patients, though his absences from home have unforeseen consequences, and Morwenna starts to slip away from the village in secret. Ralph enlists Tess and disgruntled locals to set a plot in motion to undo the Despards and the Poldarks.
When the banks start issuing paper notes instead of gold, Demelza finds herself thrown into uncharted waters with her workers and the locals, a situation taken advantage of by Tess and Jacka. Morwenna tackles the grief of being parted from her son, while Geoffrey Charles makes plain his intent to marry Cecily, landing both of them in trouble. George conspires once more against Ned and the Poldarks as he and his allies enact a plan to destroy their opposition for good. Drama, starring Aidan Turner.
Ross throws himself into fighting for Ned's liberty as George prepares to marry Cecily and finalise his deal with Hanson and Merceron. Geoffrey Charles is forced to make a desperate plan to elope with Cecily before the wedding, and Demelza uncovers a theft at the mine. Sam's growing attachment to Rosina comes under threat by Tess's claim to seek a purer life and with Ned's trial looming large and the odds stacked against them, Ross pleads for Dwight's help in a daring attempt to save his friend.
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. Sam continues to meet with Tess against all caution as Cecily and Geoffrey Charles plan their escape with Ross's help, but the danger that stalks the Poldarks follows swiftly.
Several months have passed and Ross has got in deeper with the French invasion force as they prepare to welcome their leader General Toussaint. Meanwhile, Morwenna and Drake are ready to welcome their baby, while George stumbles on the means to undo Ross once and for all with the help of Merceron and Hanson. Ross and his friends must launch their most daring plan yet to try to save themselves and the country from enemies both at home and abroad. Last-ever episode of the drama, starring Aidan Turner. Last in the series.