His long-running feud with George Warleggan (Jack Farthing) continues apace but Ross will face another sinister foe in the form of rival politician Monk Adderley played by Max Bennett.
Says Turner: “‘Monk represents everything that Ross hates, he is corrupt and has likely acquired his political position through nepotism rather than hard work, Monk is mostly involved in politics for the social scene and rarely bothers to show up to the House of Commons.
“Ross and Monk immediately get off on the wrong foot and it is funny to play that situation where you just don’t trust someone from the get go – he doesn’t trust Ross and Ross doesn’t trust him. They clash straight away and whilst it is never really spoken about, they have this unsaid hatred for each other from the very beginning until it reaches a dramatic end.”
Alongside all the returning favourites is another new character, Lady Whitworth, the mother of odious cleric Ossie. She will be played by veteran actress Rebecca Front.
Executive producer Karen Thrussell said: “In this series Ross and Demelza will face new challenges and try to turn their backs on old ghosts. Ross strives to become a better man, but his dark and reckless streak is never far from the surface and will lead to him facing new enemies and suffering great losses.”
Horsfield added: “Winston Graham was writing about a real marriage, not a rose-tinted starry-eyed version of one – but that’s what makes it all the more rewarding to bring to the screen. The reconnection between Ross and Demelza, the renewed passion, the forgiveness and redemption of their marriage has been hard won, and is therefore all the more to be valued and enjoyed.”
Poldark season four starts on Sunday September 30 at 9/8c, Masterpiece on PBS
Sign up to the Radio Times newsletter for the latest TV and entertainment news