Poldark's series 3 finale is the “lowest point” for Ross and Demelza says writer Debbie Horsfield

Especially when this happened:

So what does it all mean?

Fortunately we were able to speak to Poldark scriptwriter Debbie Horsfield who is clear on one thing – Demelza did sleep with Hugh.

“To me it’s clear something did go on in the sand dunes,” she says.

“It’s never discussed. Ross never asks and Demelza never actually tells him. They will work through that particularly rather large bump in the road in other ways. But it’s never explicitly discussed.

“It’s a rather tragic story in the end. It’s deliberately ambiguous although many viewers will draw their own conclusions but it’s interestingly the lowest point of Ross and Demelza’s relationship.

“Although by the end of the series hopefully we will feel as a viewer that there is a long journey to go on but that there is still hope.”

What about the episodes to come?

“Without wishing to spoil anything, the books tell the story of an enduring marriage and it’s a very realistic marriage. Ultimately the people in it are bound together by mutual love and respect abut that doesn’t mean they don’t encounter a lot of challenges on the way. These last few episodes we have seen them really grappling with what it means to deal with an encounter with those challenges which are not always easy.”

Demelza’s return to Nampara – and her marital bed – at the end of the series finale is hugely significant, adds Horsfield.

“In the end she has come back. It’s very clear she has made a choice. If that wasn’t the choice she made there would be no coming back.”

As to why Demelza did what she did, it seems as if events cruelly conspired to lead to what Horsfield suggests will be a one off.

“She was attracted by the courtship side of things. Ross doesn’t like poetry, that isn’t why she fell in love with him. But I think if Hugh had turned up on a different day in different circumstances, possibly it would never have happened. It’s the perfect confluence of circumstances.”

Demelza, of course, has been tempted before with Captain McNeil in series two, but this, Horsfield adds, was different.

“Captain McNeil shows it wasn’t about revenge or payback and she certainly wasn’t doing it for that reason now.

“Some viewers and readers would love to think it’s all about revenge on Ross but for me that’s not her character and the way she deals with McNeil shows that it’s not her character. She’s not a vengeful person.

“I think her heart is engaged by this man in a way which surprises her. Obviously it’s only ever been Ross. As she goes on in the books to contemplate why it happened she in many ways can’t account for it herself. She can’t give any one reason why it happened.

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“People say Ross is guilty of neglect but it’s just one element in a lot of things. She and Hugh are around about the same age, Ross is ten years older and there’s a kind of generation gap thing where she’s enjoying having a fun time with someone who’s her own age but it’s not the one reason. In some ways, it’s a contributory reason.

“Events made this the one and only time it could ever have happened. She has no intention of it happening again.”

So there we have it…

Poldark will return to BBC1 with series four in 2018. What's going to happen? Listen to our podcast to hear our five major questions...