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.

A cheerless Christmas looms for the Poldarks with Francis drowned in the mine having only found fool's copper and Ross facing debtor's prison if he cannot pay Warleggan. Ross is also anxious to expose the traitor and agrees to a dangerous scheme to trap them whilst Demelza is troubled by his frequent visits to console Elizabeth - though Warleggan is quick to ingratiate himself with the widow. Ray Penvenen accuses Dwight of fortune hunting and tries to ban him from seeing Caroline but she is far too perceptive and realistic to give up the man she loves. She also bails out Ross, whose tenacity she admires, in his hour of need - whilst seeking to remain anonymous.

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.

The mine is at last bringing Ross wealth but Demelza, still slow to forgive, goes to stay with new mother Verity. An angry Ross gives the snide Warleggan a beating after his suggestion that Ross is cheating Elizabeth's son out of his inheritance before deciding to reenlist to fight in the Napoleonic wars. Dwight also signs up as a naval surgeon but is reunited with Caroline before he sets sail. Warleggan builds fences around his property, cutting off the public right of way and Demelza is one of the casualties of his hired thugs. Irate locals march on his house, Trenwith, vowing to burn it to the ground, but Ross dissuades them to spare them prosecution before he is reconciled with Demelza.