We open in a ravine, where Ross has regained consciousness after his blow to the head. Meanwhile, Demelza, Sam, and Drake are searching for him, hoping to keep it quiet that he’s missing. But according to Sam, Tess knows – which means that everyone else soon will, too. She means well, Sam insists. Demelza and Drake aren’t buying.
Cut to an awkward breakfast at Killewarren with Dwight, Caroline, and the now-widowed Kitty. Dwight assures Kitty that she and her child-to-be will always have a home with them. For Caroline, already worried that her husband is attracted to Kitty, this is an unpleasant surprise, but Kitty seems mostly preoccupied with avenging her husband’s death.
In London, Merceron arrives at George’s home to gloat over Ross’s having been “thrown down a mine.” Cary is delighted and Valentine is angry, but George is strangely unsettled by the news.
Cecily’s chaperone surreptitiously delivers a message to Geoffrey Charles. Her doors and windows are locked, Cecily writes to him, and servants are watching her every move. Help!
We check back in on Ross in a cave as he stumbles over some sacks of ore. After finding his way out, he has his injuries treated by Dwight, telling him that he is determined to go to London and expose Merceron. Naturally, Demelza must be kept in the dark. Not for the first time, Dwight thinks this plan is foolhardy and dangerous. (Take a drink, everyone!)
Later, as Demelza binds up his cracked ribs, Ross lies that he got in a fight with a gang of Frenchmen. Right.
In the village, Rosina is troubled to see Tess canoodling with Sam. Over tea with her new best friend Morwenna, Rosina confides that Tess “is up to some wickedness” and that Rosina’s father is, too. Later, Drake shares this information with Demelza: Tess and Jacka are spearheading the plot for the stolen ore. Demelza is livid, and she and Drake set off to see the stash for themselves, disturbed to find not just ore but firearms. As they hear men conversing in French nearby, she and Drake make themselves scarce.
Later, they meet up at Nampara with Ross; he and his mine captain Zacky Martin have found the stash as well. Why is it there, and who are these Frenchmen? As Demelza regards him suspiciously, Ross tells her he really should return to London and report it. She knows there is more to it than that. So does Dwight, who later warns Ross to steer clear of Merceron. Will Ross listen? (Hah!)
Naturally, Dwight isn’t going to let Ross risk his life in London alone, and he enlists Kitty to gather up evidence against Merceron left to her by Ned, and join Dwight on the journey. And of course, Caroline has no intention of allowing Dwight to travel for days alone with Kitty, so in short order, all four of them, plus Horace, are crammed into the Enyses’ carriage on their way to London.
Ross pays a visit to Merceron, and is not surprised to find Hanson there. Veiled threats are exchanged, and Ross learns that Wickham might not be trustworthy either – he is Hanson’s half-brother.
Ross’s next visit is to Wickham – why wasn’t he told of his connection to Hanson and Hanson’s connection to Merceron (apparently, they are also half-brothers)? And isn’t it a big deal that Merceron tried to have him, Ross, murdered? Wickham is skeptical of that claim. Ross tells him of the arms hoard in Cornwall, but his public defense of Ned has destroyed any credibility he had with the Crown, and Wickham coldly advises him to return to Cornwall and get real proof.
Maybe Ned’s evidence will help. The next day in Hyde Park, Dwight, Kitty, and Caroline circulate pamphlets accusing Merceron of allowing prison inmates to be used for medical experimentation.
At George’s home, Hanson is enraged about the pamphlets, insisting that the people distributing them be held responsible. Merceron chillingly acknowledges that the allegations are true, but don’t go far enough; the people being experimented on are “of the vilest kind.” Public opinion is turning against Merceron, and George and Cary decide to distance themselves from him, in Cornwall.
The next day, Caroline is riding alone in Hyde Park when a sinister-looking man jumps from behind a tree and spooks her horse. She is too adept a horsewoman to be thrown, but is shaken. Afterward, she and Dwight quarrel – he accuses her of foolishly risking her safety, and she claims he’s getting too close to Kitty. Kitty suddenly appears and is mortified. Dwight decides they too must return to Cornwall.
Back at Nampara, Demelza is hosting a family dinner, dismayed that Sam has invited Tess as his guest. Drake and Morwenna joyfully announce that they are expecting a child. (That was fast!) As Tess pretends to be as delighted as everyone else, Prudie confides to Demelza that she’ll be glad when Sam comes to his senses. The next day, Demelza tells Sam privately that Tess’s newfound piety is not what it seems. Sam, always seeing the good in people, doesn’t believe her. Demelza lets Tess know she’s on to her, but Tess, feigning innocence, has latched on to Sam and isn’t letting go.
At Trenwith, George and Cary’s plan to put some mileage between themselves and Hanson and Merceron backfires as they get some unwanted houseguests. Guess who? Merceron wants the smear campaign against him stopped, and since “the Hyde Park incident” was not sufficient, he “must devise a worse deterrent.” If George was uncomfortable before, he is now really disturbed – this is spinning out of control.
As he is packing at his London flat, Ross gets a visit from Geoffrey Charles and Cecily (how he freed her, we don’t know). Can Ross help them? Ross shepherds them back to – where else? Nampara. Geoffrey Charles and Cecily will board a ship to America leaving that night and Ross will row them out to it after dark.
At Killewarren, Caroline runs across Dwight’s notes on George’s insanity case, and is caught red-handed by Dwight as she is reading them. He is furious, and orders her to forget she ever saw them. A few minutes later, she is looking for Horace and calls out to a servant in the shadowy foyer. But it isn’t a servant, and as the front door slams, she finds Horace lying motionless on the hall floor. While treating the dog, Dwight suggests that Caroline’s indulgence of Horace is to blame. But Caroline knows better…
…Cut to Trenwith, where Caroline angrily confronts George and Cary: her dog has been poisoned, and the same person is responsible for the incident in Hyde Park. Cary tries to patronize her, but she isn’t having it. Glaring at George, she posits that “a person of great eminence” who has been treated for lunacy would be ruined if the word got out. To keep that from happening, they must promise that “their friend” will never trouble the Enyses, Poldarks, or Kitty Despard again. Cary has no choice but to agree. After she leaves, George wonders why they are “protecting some local lunatic.” “We’re protecting you,” Cary tells him disgustedly.
Ross sets off to prepare the rowboat he’ll need to transport Geoffrey Charles and Cecily to the ship, but is ambushed on the beach by several armed men. He is marched into the ore cave, where he encounters someone vaguely familiar: it’s the Shady French Official who shook down Ross for bribes at Quimper Prison in season three! Ross evaded him then, so he is determined to dispatch him now. (Talk about holding a grudge.) Ross manages to convince him that as he (Ross) is persona non grata in London, he’s switching his allegiance to France, and might be useful to their cause.
Meanwhile, Demelza is down at the cove, searching in vain for Ross. She is met by Drake, who offers to row “the lovebirds” out to the ship. She goes back to fetch them, but in the yard, they are overpowered by Merceron’s men, who carry off Geoffrey Charles and Cecily and leave Demelza bound and gagged in the stable. In the barn, Geoffrey Charles is beaten within an inch of his life. Too bad, as George is at that moment sliding a big check across the table to Merceron, telling him that he and his cronies must lay off Geoffrey Charles, the Poldarks, the Enyses, and Kitty. But it’s a no-go: Merceron is more interested in revenge than money.
Prudie finds and frees Demelza, and a heartbroken Cecily finds a bloodied and unconscious Geoffrey Charles. He’s alive, Hanson tells her, but if she tries to run away with him again, his thugs will finish the job. To save his life, Cecily knows she must end it with him. As she later dresses his wounds, she tells Geoffrey Charles that she values her freedom, and “doesn’t wish to be any man’s wife.”
In the morning, the Shady French Official is skeptical but lets Ross go. Ross conceals what happened from Demelza.
Dwight assures a grateful Caroline that Horace will make a full recovery. They are interrupted by Kitty: it’s clear that she has outstayed her welcome. The following day, on board a ship, Kitty reassures her friends that Ned left her the means to live and raise her child. But she will also have company: Cecily. As Ross and others watch for Merceron’s thugs, Cecily boards the ship, telling Geoffrey Charles goodbye: he must forget he ever knew her. And she and Kitty sail away to Jamaica. You just know they’ll form a feminist-abolitionist collective somewhere.
Demelza tries to comfort Geoffrey Charles: “There will be other loves.” (Read Winston Graham’s novels if you want to know if she was right.)
Ross asks Dwight to look after Demelza in the coming months – his actions “may seem strange” to her and everyone else; it will be the “greatest gamble” he’s ever undertaken. He then meets up with the Shady French Official and they gaze out to sea, anticipating a French invasion. What is Ross up to?