In brief, it is the story of Ross Poldark, coming home to Cornwall from fighting in the War of American Independence, tired and injured. When he returns, he learns that his father is dead, his estates are virtually bankrupt, his fiancee believed him dead and is now engaged to another. Born into a family of good lineage, if not riches, Ross is part of the landed gentry of Cornwall but has a compassion for those less fortunate that constantly gets him in trouble with his peers. It is one such impulse that causes him to rescue an urchin from a group of bullies; when he realizes it is a girl, he agrees to hire her as a servant.
I remember at this moment saying to my mother, "Julian and Tibby!" a reference to Dawn's Early Light, book one in perhaps my all time favorite series, Elswyth Thane's Williamsburg Novels, and she protested, "No!" in horror because she loves those books so much but there are some similarities. Both Julian and Ross fight in the Revolutionary War, and are very much influenced by the ideals of liberty and equality for men: Julian in the years after his arrival in Williamsburg from England in 1774 and Ross upon returning to Cornwall from the Colonies, both men in love with beautiful women from the upper levels of society, both men poor but determined to survive (Ross is much less law abiding than Julian), and both take an initially paternal interest in a teenage girl from impoverished family.
Indeed, I hope I have persuaded you to try the Poldark novels or the DVDs, and I have now convinced myself I need to own and reread the entire series! Other Winston Graham novels were made into movies and are also worth hunting down - notably Marnie (Hitchcock) and The Walking Stick (a compelling but sad book).