This recap contains spoilers for Outlander Season 3, episode 3, "All Debts Paid."

Episode 3 of Outlander Season 3 is a pretty big deal for fans of Diana Gabaldon's novels: Not only does it reintroduce a pivotal character in Lord John William Grey (all grown up and decidedly more dashing than the last time we saw him in Season 2, now portrayed by David Berry), but also closes the chapter on Claire and Frank's tumultuous relationship in surprisingly poignant fashion.

While the show has to omit or streamline countless plot points from the novels in the adaptation process — including cutting Jamie's trip out to the seals' isle (although perhaps we'll see it later in flashback) and the many prickly layers of his complicated relationship with Lord John — for the most part, Outlander's writers do an admirable job of staying faithful to the emotional arcs that drive Gabaldon's novels. That's especially true of episode 3, written by Matthew B. Roberts, which takes our heroes on a believable and equally effective journey, even if the signposts are a little different along the way.

But "All Debts Paid" also featured a massive change to the narrative of Gabaldon's Voyager — one that will have ripple effects across the series — and we couldn't be happier about it.

In the books, Murtagh FitzGibbons Fraser, Jamie's godfather and right-hand-man, is killed at the Battle of Culloden, but episode 3 reveals him to be alive (if not well) at Ardsmuir. When the prison is closed, the fan-favorite character, played by the indispensible Duncan Lacroix, is shipped off to the American Colonies with the rest of the prisoners, while Jamie is taken to an estate called Helwater to serve Lord Dunsany.

Showrunner Ron Moore tells Mashable that there was one very good reason why he chose to keep the beloved character alive: "Murtagh’s development in the series is different than the books basically from the beginning. We made him much more of a key player in the story, much closer to Jamie, and then he got in on [Claire's] secret in Paris. He became part of the family in a different way than in the books. And I just wasn't ready to let him go in Culloden. He is going to survive and we will catch up with him later, we will just keep him going."

Fans who've read book four might have some idea how Murtagh could come back into Jamie's life, but that's a discussion for another day.

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Back in the future, we see Claire's relationship with Frank fracture beyond repair. The episode's early moments reveal that Frank has been seeing other people, since Claire can no longer love him the way she did before, and while their agreement seems amicable at first, over the years, the connection between them deteriorates to the point where Frank decides he wants a divorce so that he can take Brianna back to England without Claire, to start a new life with his mistress — a suggestion that naturally incenses Claire.

(Sidenote: I hope the TV Academy and HFPA will finally pay attention to Outlander next awards season — over the course of these first three episodes, Caitriona Balfe, Sam Heughan, and Tobias Menzies have all done a spectacular job of establishing the passage of time through their nuanced, perfectly calibrated performances, conveying the agony of grief, insecurity and old wounds more effectively than any old age makeup or hair change could. Heughan's powerful, restrained delivery when John touches Jamie's hand effortlessly evokes all the trauma he suffered while at Black Jack's mercy in a single expression, while Balfe and Menzies' confrontations are searingly honest, loaded with the weight of two decades' worth of unspoken resentments.)

Unfortunately, Frank never gets the chance to start over, because he's killed in a car accident following the fight.

According to Balfe, Claire manages to be content in a marriage of convenience for so many years because she experienced true love with Jamie — but things aren't quite so simple for Frank.

"She's sort of decided within herself that once was enough for her, and that the memory of that love is enough to carry her through the rest of her life. Her marriage with Frank, yes, it's a marriage of convenience, but I think it's a marriage of friendship in some ways," she tells Mashable. "They come to an agreement where she won't ask any questions, he can do what he wants. She's going to focus on her career and being a good mother, and he's going to be a good father. It works for them, and it works for 20 years. And really the tragic victim in that marriage is Frank, because he's somebody who really wants Claire and still is in love with Claire and still desires her, but she just can't reciprocate it."

She adds, "Everyone gives Frank such a bad rap, but if you're in that marriage, I think he can't help but try and find the things that he needs outside of it. Claire still has Jamie's love inside her heart, so she's good."

As emotional as Claire's farewell to Frank is, Balfe reveals that filming the hospital scene presented an unexpected challenge.

"Our first take, I look down and realize that sound had stuck a microphone to Tobias' bare chest. That was not very emotional. I was like, 'Um, does the dead guy need a microphone?'"

Despite the technical difficulties, Balfe adds that the scene was incredibly important for Claire as a character.

"At that point they were so emotionally far apart from each other, and the intimacy had been gone for so many years, but it's like you don't realize how much you love somebody until they've been taken away from you," she notes. "They've been so used to living in this side by side world, but taking each other for granted, in a way, that at that moment she just realized that, there's always been this huge love for [him]... It's an apology."

Tobias Menzies has now said goodbye to both his characters, Black Jack Randall and his descendant, Frank, but admits that he doesn't exactly feel emotional about losing either:

"It's sort of odder than that, because they're all just like bits of you, so they don't go anywhere. Will I miss playing them? Yes, it's been great. It's been an amazing ride. And I'll also miss all the great friends that I've made on it. But it's been fun to go on and do other things. We've been doing this for three and a half years now. But yes, I'll definitely miss it, and it's been a really great adventure."

Outlander airs Sundays at 8 p.m. on Starz.

Watch: 'Outlander' Season 3 is a heartbreaker