This Is Us star Justin Hartley previews 'emotional and dangerous' Big Three trilogy

We can think of three good reasons why you may be interested in the next three episodes of This Is Us: The Big Three.

The final "trilogy" kicks off tonight, and by that we mean, the annual tradition of three consecutive installments of the NBC family drama that spotlight a different member of the Big Three. First up is Kevin (Justin Hartley), then Kate (Chrissy Metz), and finally Randall (Sterling K. Brown). All three episodes will focus on the decisions that the siblings decide to make in the aftermath of Rebecca's potent address to her children at the cabin, in which she urged them to take big risks and not make their lives "smaller" as she battles early onset Alzheimer's.

"You're going to see the impact that had on the three kids and what they choose to do because of that very powerful speech," Hartley tells EW. "[They're] very clear about what she wanted — until they go to do it. And that's one of the things that happens in the episode: Kevin has this idea of what his mom wants, and he's on a mission, like, 'Okay, this is going to be my thing.'" And after a surprising, devastating event, "he discovers a really beautiful part of himself through all of that tragedy," continues Hartley. "All three kids do that [in their spotlight installment]."

What words would Hartley use to describe this trilogy as a whole? "Seminal. I would say that they are significant and emotional and dangerous. Each character is making a decision that is going to change the course of their life from here. So it's a defining moment — a line in the sand kind of thing. These characters that we've seen for the past six years are all of a sudden leading different lives, which is kind of cool."

In tonight's episode, Kevin heads east with the twins to spend time at the Pearson cabin with Cassidy (Jennifer Morrison) and Uncle Nicky (Grifin Dunne), who are spearheading the construction of the family "mecca" that Kevin is funding. There may be some hiccups in that process, but they pale in comparison to what will unfold with Cassidy. "These people came together in times of tragedy — they all had their own stuff going on — and it comes to a head and it boils over sometimes," he says. "Kevin, in hanging out with Cassidy, has this idea that everything's okay or it's better when they're together. He doesn't quite understand how dark her darkness gets."

Meanwhile, the ever-evolving Nicky proves to be an unlikely source of great wisdom for Kevin. "Look, the weirdest person in the world to be able to give him advice is Nicky, but he does it," says Hartley. "And he gives him some of the most important advice."

Next week's episode features Kate at a crossroads in her life. With her marriage to Toby (Chris Sullivan) faltering, she heads north to San Francisco to spend critical time with him. "Kate, in a weird way, is finding herself in a place that Kevin's been in before — she's trying to figure out how to make this marriage work and come to the realization that some things don't work out the way that you thought that they would," he says. "Do you adapt and adjust? Or are you even able to do that and you have to move on?" (Based on the flash-forward to her second wedding that viewers glimpsed in the season 5 finale, you probably have a few ideas.)

Last and far from least is Randall, who, like the audience, was taken aback by Rebecca's decision to choose Kate as the overseer of her care should husband Miguel (Jon Huertas) not be around to help. In the concluding trilogy episode — which, by the way, Hartley directed — Randall will have an important conversation with Rebecca, and his promising political future, which was teased in that wedding flash-forward, will start to come into focus. "Randall is on this journey with his mother and he's always been the one that took care of her," says Hartley. "She's explained to him that it's his time to take care of himself now. There are maybe greater things that he can affect more people than just one, and he might be able to do some things that can affect an entire nation or a world. And he certainly can't do those things if he's hindered by the things that he's allowed to hinder him in the past. It's a really moving episode. I can't wait for everybody to see it."

You can see the first of these three episodes tonight at 9 p.m. ET/PT, and you can watch the first minute of tonight's installment in the exclusive clip above.

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