'Outlander' Season 7, Part 2 Preview: On Set With Caitriona Balfe, Sam Heughan, and the Cast (Exclusive)

"It was honestly one of the most difficult episodes I filmed in a while," says Caitríona Balfe about a shocking decision made by her character, time-traveling 20th-century surgeon Claire Fraser, in the second half of Outlander 's seventh season. "[I'm still] wrapping my head around some of the stuff that came from the book that Claire does."

It's April, and we're on set in Scotland, where Diana Gabaldon 's best-selling novel series has been brought to life as an epic historical drama. (The Starz fantasy is now telling the story of her seventh and eighth books, "An Echo in the Bone" and "Written in My Own Heart's Blood.") Since the show's 2014 debut, Balfe has won hearts playing the smart, practical Claire, who falls through time and marries 18th-century Scottish Highlander Jamie Fraser ( Sam Heughan ). Their adventure-filled love story will wrap with the eighth season, which was in production during our visit (we're sworn to secrecy). As for the scene in question, Balfe says, "I think I made it believable."

But things aren't so fraught for Claire when the story picks up where the mid-season finale left off. She and Jamie, along with their nephew Ian ( John Bell ), return to the bonny shores of 1778 Scotland from the war-torn Colonies with the body of Jamie's second cousin, British general Simon Fraser ( Angus Macfadyen ). And not all is well at Lallybroch, the home of Ian's parents, Jamie's older sister Jenny ( Kristin Atherton , taking over the role from Laura Donnelly) , and her husband Ian Murray ( Steven Cree ). But "they're going to find that things have shifted since they left Scotland," says Maril Davis, an executive producer with Matthew B. Roberts. "It's a bittersweet time." Firmly in the "bitter" category is someone who's always been a problem for Jamie — his ex-wife Laoghaire ( Nell Hudson ). "Jamie and Claire have some unfinished business with [her]," reveals Roberts. And she's as vindictive as ever.

Hudson isn't the only face from past seasons to reappear. Jamie's uncle Dougal MacKenzie ( Graham McTavish ) and evil time-traveler Geillis Duncan ( Lotte Verbeek ) are also back, but it's unclear how, as both are long dead. Hey, in a show about time travel, strange things are inevitable.

Also inevitable on Outlander is that Claire and Jamie become separated due to outside forces. This time, old friend Lord John Grey ( David Berry ) begs Claire to go to Philadelphia and tend to his ill nephew Henry Grey ( Harry Jarvis ). Grey, a British army officer and diplomat, and the Frasers have crossed paths many times, and in many places. As a governor in Jamaica, John saved Jamie from arrest by the British. On Fraser's Ridge, Claire saved John, nursing him through measles. John offered to marry Brianna Fraser ( Sophie Skelton ) to save her from a siege of suitors. Their biggest bond was formed when John agreed to raise Jamie's illegitimate son William as his own.

Grey now sports an eye patch in the seventh installment of Outlander. It's not a fashion statement. It's the result of almost losing his eye after a brutal beating. How he gets that injury, who inflicts it and why are threads that run into the final season. Berry asserts that in the second half of Season 7, Lord John "has a very pragmatic agenda, which is to safeguard the Frasers."

Always loyal, Claire agrees to Grey's request. She's accompanied by Ian, whose sweetheart back in the Colonies, Quaker Rachel Hunter ( Izzy Meikle-Small ), is in the crosshairs of the vengeful Arch Bug ( Hugh Ross ). He's vowed to get back at Ian for mistakenly killing his wife. That threat "is one of the reasons Ian has kept himself from opening his heart to Rachel. We're going to see what happens to our two young lovers," Davis promises.

But it's not only Rachel whose life is at stake. Soon enough, "Claire's in peril," Balfe reveals. That leads to the fateful choice the actress alluded to struggling with earlier. When Claire reunites with Jamie, "what has just happened has complicated that [reunion] incredibly," Balfe tells us. Heughan teases a bumpy road ahead for the couple: "They work through it. But it's tough. It's going to be an interesting storyline," the actor says.

On the day we visited the set, Heughan was shooting a scene where Jamie makes a discovery in the woods that will send shivers up your spine. But no matter how dangerous, brutal or ugly the world around them gets, the Frasers keep their love alive. In this season, Heughan says, "The passion hasn't changed. It's deeper and it's developed." The undying ache that the soulmates have for each other as they mature is one reason fans keep coming back. "What's cool about the show is that we go to that place where we can say that love isn't just for teenagers and 20-year-olds," Roberts says. "That passionate feeling—that you need to be around somebody, and all the hormones are kicking off—that can last a lifetime, especially if you nurture it and you pay attention to it. That's what Claire and Jamie teach us. They pay attention to each other."

Jamie will also have to finally deal with his adult son William (Charles Vandervaart), who's been raised by Lord John and doesn't know his true parentage. Heughan hints at "a difficult storyline for those two."

Let's just say there's no Father's Day card for this situation. "William has been through the wringer this season," Davis adds.

Meanwhile, as soon as Claire's out of one crisis, she heads directly into another. She and her new Quaker doc pal, Rachel's brother Denzell Hunter ( Joey Phillips ), manage a Revolutionary War field hospital. ("It was bloody freezing!" Balfe exclaims when recalling the outdoor February shoot.) The pair must deal with a potentially fatal injury that requires a delicate surgery. An entire prosthetic rig was built to show the operation. "It's always quite fun when you get to do a little bit of all the blood and guts and gore," Balfe says. "A very interesting visitor comes and helps."

As the war unfolds, Jamie runs into George Washington again and is even promoted to brigadier general, but the Scot has mixed feelings about serving. Balfe hints, "He fulfills his obligations. First and foremost, his obligation is to Claire."

After all, strong marriages run in the family—and so do unforeseen, heartbreaking farewells. Jamie and Claire's daughter Brianna and her husband Roger ( Richard Rankin ), living in 1980s Scotland, were torn apart in the midseason finale. Their young son Jemmy (Matthew Adair ) was kidnapped by Bree's duplicitous colleague Rob Cameron ( Chris Fulton ), who they believe took the child back through time so he could lead him to a cache of stolen Jacobite gold.

A desperate Roger pursues them through the stones to the 18th century and hunts for Jemmy with help from his ancestor, time-traveler Buck MacKenzie (Diarmaid Murtagh). Buck, let's remember, tried to have Roger executed by hanging in the Colonies, and frightened Roger's kids in the 1980s when he mistakenly time-traveled there.

"They are an odd couple who come to grow really fond of one another," Rankin says. "Buck has a lot of MacKenzie in him. Determined, honorable, heroic at points. Roger couldn't have gone through what he goes through in [these episodes] without Buck. He's very grateful." And Roger goes through a lot. You could call it the shock of a lifetime in a lifetime of many shocks.

Back in the 1980s, Brianna's about to get a shock too. "She's just so deflated. Roger's now gone through the stones. Jem's gone. She doesn't know if she'll see either of them ever again," Skelton says, as she perches on the steps of a house that will be a happy sight for fans. "She's lost her world, her family, which Brianna's never had much of anyway." Then a surprising threat appears and "she hits this fight or flight moment, and decides to fight."

Davis hints at a fierce Bree, saying, "The Brianna we see in the second half is Mama Tiger. We're going to see her take her future in her own hands near the end of the season."

Speaking of the end, there's a jaw-dropping cliffhanger you won't see coming, according to Balfe. "The last scene...occasionally you get scenes where you get goosebumps. Even [talking about it] now, it's really powerful," she says, recalling filming the moment, which is set in a church. "There's certain things that when you filmed them, they are in your mind. That feeling never leaves you. So, when we went to film [the ending], I got this bolt of a memory. It all feels very like, 'Ooh, spooky.' [Claire thinks] how can it be? How's it possible?"

And what about the final Season 8? Balfe says "[Season 8] is probably the season I've known the least about going into it. I have no idea how the season ends. We only got the scripts for Episodes 1 and 2 about two months before we started. We would usually have more [time]. I don't think [the producers] trust any of us, to be honest. [Laughs] I think they're trying to keep things very, very close to their chest. We are as excited and nervous and curious to see what's going to happen as everybody else."

Heughan adds, "There's just so many ways that we could finish the story. We want to make it right. We've had a lot of discussions. We've put in our two cents. Everyone's got their own version of how they want it to end, from the fans to the producers to the writer. And I actually think there might be multiple endings from what I hear." It's Outlander, just about anything is possible.

Outlander, Season 7B Premiere, Friday, November 22, 8/7c, Starz