[Warning: This story contains spoilers from Thursday's episode of Vikings, "Portage."]

Over the course of four seasons, Vikings has proved time and again that when it comes to death, the show isn’t afraid to say farewell to some of its more important characters. On Thursday's episode, Ragnar (Travis Fimmel) continued plotting his comeback against his brother Rollo (Clive Standen), while over in Wessex King Ecbert (Linus Roache) looked toward expanding his empire.

Both storylines culminated in two notable female deaths: Ragnar had had enough of Yidu (Dianne Doan) and her “medicine,” and so he put them both out of their misery by a surprise drowning, while Kwenthrith’s (Amy Bailey) supposed ally Judith (Jennie Jacques) stabbed her in the back while she was attacking Ecbert.

According to showrunner Michael Hirst, these deaths are just the beginning of what’s to come. With only two more episodes before the show wraps for its fourth midseason finale, The Hollywood Reporter caught up with Hirst to see how these ladies’ deaths will affect their killers, to preview Ragnar’s next moves and to tease Ragnar and Rollo’s ultimate showdown.

What does Yidu’s murder represent for Ragnar?

I was originally imagining that it would be a love story, and what actually happened was that it wasn’t a love story. Ragnar — and Travis agreed with this — was no longer in the market for a love story. He needed someone to talk to, someone who didn’t know him. Yidu herself was a complicated person and she, although he in theory set her free, didn’t feel free. In order to keep him close, she got him hooked on drugs and made sure that he needed them as a way to stay alive and feel stay safe and in his orbit. ... Killing her was a way of trying to free himself from his dependency on her and on the drugs.

Was there discussion about having his sons witness the murder?

It wasn’t supposed to be in front of his sons, but it’s a terribly shocking moment and scene. Ragnar is a Viking and it’s one of those occasions when a contemporary audience has to swallow that. The Vikings saw terrible things and in many cases did terrible things. From Ragnar’s point of view, it’s part of them growing up. I hesitated to put it down on paper because I thought it would shock everyone so much. To some extent it was Travis who persuaded me that I needed to be brave enough to put it in and that it was perfectly in keeping with the story arc. Ragnar’s story is becoming obviously much darker now.

How does a drug-free Ragnar affect his game in Paris?

His going cold turkey is part of the story going forward; his struggle with not depending on the drugs and facing up to what has to be faced up to. Having dug into that storyline, it’s not something that I was likely just to skip over. We do see the consequences of him trying to get off the drugs and coping with reality again, and it’s not an easy process.

Did it always have to come down to brother versus brother for you?

I think so. There was never any way that Rollo was going to go away without having a final showdown. I knew from the start that of all the Vikings Rollo had the best end game. I remember talking to Clive probably in season two when he said, “I‘m a drunkard, I’m a loser for staying, I’m bitter, I’m angry. Does this keep happening?” And I said to him, “Yeah, it does keep happening until it doesn’t happen anymore, and I’m not going to tell you what happens to you, but if I told you, you would go and dance naked on the sand.” That’s the same line I gave to The Seer (John Kavanagh) eventually. But it was always going to be a finale really between them, and as Ragnar says, to Yidu he’s not going to Paris to plunder and he’s not going to prove himself anymore. He’s just going for Rollo. He has to deal with the situation with his brother even though he doesn’t want to. But he knows that he has to do it.

In Wessex, King Ecbert finally got rid of a foe in Kwenthrith. Was there any other ending possible for that character? She’s one you took some historical liberties with, correct?

The whole Mercian dynasty and the in-fighting between the Mercia royal family is very complicated and took quite a long time, so it would have been excessively boring for everyone if I had just trotted that out, so I did make big decisions about which Mercian kings and queens I wanted to concentrate on. But there wasn’t really any way of her having a happy ending because the fact was there were no happy endings for the Mercians. In any case that story had kind of run its course. Ecbert’s big plan was to be king of kings, to take over the whole kingdom of England and pass it on to his son. So one of the logical things he has to do is to take over Mercia. I wanted Kwenthrith’s death to be meaningful and powerful. The fact that it eventually involved Judith was also very good for the general story. So I was actually very pleased with both deaths. I think both deaths are quite shocking in their own way, but totally plausible and believable and part of a much bigger story.

How does having bloody hands change Judith?

Judith has been quite a moral presence, which has been a good check on Ecbert’s deviousness. Obviously she’s part of it now. She understands a lot more about how things happen. She’s a little like Athelstan’s character, who started out as a very minor character but became too indispensable to drop. Of course although he’s dead, he never goes away. I wasn’t thinking very hard about Judith when she first came into the story and married Aethelwulf. She was a very minor character but suddenly she’s become really interesting. She’s very independent minded and challenging, so she’s good for Ecbert because she can argue with him and counter him. She wants him to treat her as an independent person, which was completely unusual in that society. So she continues to be a very important character moving forward.

How will Harbard’s (Kevin Durand) second exit affect Aslaugh (Alyssa Sutherland)?

I felt more sorry for her over the whole visitation. I think it really broke her in some ways and affected her deeply. Here’s a woman who feels intensely isolated, who doesn’t have a great relationship with her husband, has a very complicated relationship with her son Ivor, and felt that this guy had come from the outside and was a force of good in her life. Leaving aside the question of whether Harbard is or isn’t a god, his behavior is difficult for her to accept at a human level. It’s very devastating and it leaves her in a bad place. Aslaug has become a much darker character as she’s embraced her Viking roots this season. Yet, of course, she’s still a human being and her jealously and her pain were very evident. I feel for her. At the end she actually becomes a much more sympathetic figure and who would have said that when she first appeared and took Ragnar away from Lagertha?

Next week’s episode is titled “Death All 'Round.” How much bloodier will these last two episodes before the midseason break be?

Well there are more deaths ... I don’t want to give more away than that, but obviously we’re looking towards the very big showdown between Ragnar and his brother Rollo. Basically in that final showdown everyone’s lives — all our major characters' lives — are on the line.

Vikings airs Thursdays at 10 p.m. on History.

What did you think of Yidu and Kwenthrith’s deaths? Sound off in the comments below.

Twitter: @amber_dowling