SPOILER ALERT: This story contains details about tonight’s This is Us episode “Vietnam” on NBC.

In a bold and fresh move, tonight’s This is Us episode “Vietnam” focused entirely on one backstory: the historical brotherly love between Jack (Milo Ventimiglia) and Nicky (Michael Angarano)–a relationship fans have been desperate to explore since we first learned of Nicky’s existence, and his mysterious death, last season.

In this episode we finally see some hint of what might befall Nicky and something of Jack’s role in the war. Nicky’s been issued an Article 15, meaning he’s been cited as a danger to himself and those around him, and this begs the question, will he ultimately do something tragically self-sabotaging?

Speaking to Deadline last week following a press preview screening of the episode, Angarano said of Nicky’s impending death, “I think it’ll be a little bit surprising how dark and sad some of this stuff is, because this was a very dark and sad and violent war, and so the storyline feels like it’s very much that…I think a lot of the story is how these two men deal with the same war in very different ways.”

Tim O’Brien, Vietnam veteran and author of Vietnam short story collection The Things They Carried, consulted with creator Dan Fogelman on the authenticity of the war scenes and hinted that we’ll see Nicky deal with some mental health issues.

“Guys lost it, you’d almost be insane if you didn’t lose it [with] the pressures of it,” O’Brien said. “And Michael’s character Nicky is a medic and putting his hands in blood every day, losing people.”

Later, elaborating on O’Brien’s words, Angarano said, “Needless to say, Nicky’s not a good soldier. And I don’t think he really cares to be at all. So ‘losing it’ could mean many different things under many different guises. It depends on what perspective you’re looking at it from. Losing it might be a very sane thing to do.”

So that mystery continues, as yet unsolved. But a brief aside here on the subject of that other big This is Us question, that of ‘her’–the unknown woman first referred to in last season’s finale flash forward. For those viewers bracing themselves for a rather long wait as with Jack’s death story, rest assured, you’ll know who ‘her’ is by season’s end. And you’ll be suitably fulfilled by the result.

Fogelman told Deadline, “I believe it’s going to be satisfying…I don’t believe it’s going to be like, ‘her is a teacher at the school.’ I think it’s going to be good. I think it’s going to be rewarding. Like many of our things do, it will answer a lot of questions and beg others. But I feel very confident in the plan we’ve had for a long time.”

But back to this current episode. Spanning some 20 years of flashbacks, we delved into how Nicky got drafted due to his fateful birthdate, the brothers’ suffering at the hands of their alcoholic father, and the fact that Jack always knew about the heart condition that would eventually kill him. But in typical Jack fashion, he rushed off to war to support his brother. All in all, in excluding other show regulars here, Fogelman bravely banked on viewers’ enduring love for Jack–and it paid off with an extremely gripping episode.

“You’re asking a network television audience to really pay attention, and saying, ‘Hey, this week you’re going to go and experience a very different episode of the show. I think you’re going to like it, I think you’re going to learn some stuff,'” Fogelman said. “Hopefully you’re snapping a finger at the audience and saying, ‘Never get too comfortable.’”

In another big departure for the show, Fogelman took the shoot away from a studio setting and into the action of a Vietnam firefight. Early in the episode, we see Jack’s fellow soldier get his foot blown off by a landmine, which connects us to the story of the amputee veteran (Charles Robinson) we saw Kevin (Justin Hartley) track down at the end of the last episode. There will be more to come from that veteran character too, Fogelman promised.

The Vietnam scenes in this episode were filmed almost entirely stateside, Fogelman said, but still, “There are a whole new set of challenges when you’re outside of the Paramount lot all of a sudden.” However, in a few days, Ventimiglia, Hartley and Melanie Liburd (as Zoe) will head off to Vietnam to shoot more of Jack’s backstory and Kevin and Zoe’s journey to uncover Jack’s past.

As tonight’s episode opens, it’s 1971, and a military-uniformed Jack is getting off a helicopter in search of his brother. “I hope you find him,” the pilot says. So we know right away that poor Nicky is in some trouble and Jack has come to the rescue. Soon enough, as we quickly flash backwards, we also learn that this is their typical dynamic: the sensitive, somewhat maverick Nicky and his superhero protective brother Jack. In fact, their pet names for each other are ‘Clark Kent’ and ‘Superman’ respectively.

We see the bothers as small children intervening when their father Stanley (Peter Onorati) bullies their mother, with Jack standing in front of Nicky to save him from his father’s ire. We see them as young men–Nicky is just 19–nervously watching the draft lottery together on television in a bar, away from their father’s unwelcome commentary. Nicky’s birthday–October 18th–is picked early on, so it’s certain he will go to war.

“Make me proud” is Stanley’s only comment later that night, but Jack of course has other plans and whisks his brother away on a “camping trip”–AKA an escape mission to Canada. But, tired of hiding behind his ‘Superman’, Nicky sneaks away from Jack the night before the planned border crossing, leaving a note that it’s his turn to “save the day”. He’s decided to face his Vietnam fate.

But of course Jack won’t let his brother go it alone for long. There he is getting a check-up with the family doctor, and we learn why Jack wasn’t included in the draft at all–his lifelong tachycardia condition. Sighing, the doc teaches him how to cheat the military medical (some push-ups right beforehand apparently), and off Jack goes. But we know it will be to no avail, because of course we already know that Nicky dies in Vietnam.

We head back in time once again, this time to the hospital on the day of Nicky’s birth, which occurs at 11.58pm on October 18th–those two minutes shy of midnight fating him to his lottery pick, and thus to die in the war. We see a roomful of babies in incubators all born on that day. All the baby boys in there will be sent to war in 19 years’ time, and in a classically emotive This is Us moment, we take in the tragic accident of their birthdate as the camera roves over the babies’ medical tags.

We also see a very young Jack with the then-teetotal and kindly Stanley waiting in the hospital for Nicky to be born. Jack’s hip flask-toting grandfather shows up and offers Stanley a swig. “You know I don’t drink” he snaps. So there’s the generations-old foreshadowing of the alcoholic legacy we know Jack will ultimately tackle.

We’ll have to wait a little while before returning to the Jack-Nicky story however. “We have a direct pick-up coming a couple of episodes later,” Fogelman said.” The continuation of that story is the rest of the storyline of that season,” he said, adding, “we’re currently filming our fourth episode of the Vietnam storyline right now.”

So there will be plenty more to come from Vietnam, and with so much else in the offing this season: the ‘her’ mystery, Kate’s IVF situation, Toby’s looming depressive episode, Miguel’s backstory, Beth getting fired, and Justin and Zoe heading into the jungle of Jack’s past, Fogelman is certainly keeping us all on our toes, as per usual.

This is Us airs Tuesdays on NBC at 9pm.