Mandy Moore as Rebecca, Mackenzie Hancsicsak as Kate, Milo Ventimiglia as Jack, Parker Bates as Kevin, Lonnie Chavis as Randall in NBC's 'This is Us.'

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NBC's "This is Us" -- a drama that mixes heart, humor and a little mystery -- is this year's breakout hit

Creator Dan Fogleman said some of the show's biggest questions will be answered by season's end

CNN  — 

Earlier this year, as TV networks were picking up pilots in hopes of finding the next hit among the hopefuls, a clear trend began to emerge: families.

With ABC’s Emmy-decorated “Modern Family” aging and the success of recent newcomers like “black-ish,” the field was seen as wide open for a new family to move into the increasingly crowded TV neighborhood. Among the four networks, according to some tallies, there was at one point about 20 family comedies up for consideration.

Ten months later – and a few weeks after new fall shows have debuted – viewers have indeed made room in their lives for a new family: NBC’s heart and humor-filled drama “This is Us.”

Last week’s episode notched almost 10 million total viewers and became the first scripted show to build upon lead-in “The Voice” – NBC’s golden goose – in the all-important 18-49 demographic. It also grew its audience 13% overall from its previous airing. Simply put: “This is Us” appears to be this year’s breakout hit.

[Spoiler alert if you haven’t seen the series premiere.] The show centers on a young couple (Milo Ventimiglia and Mandy Moore) who build a unique brood from the ashes of heartbreak after one of their triplets dies during child birth. On the same day they are confronted with tragedy, another baby is brought to the hospital after being left at a fire station. The couple decides to adopt him – they call their kids “the big three.”

Justin Hartley as Kevin, Sterling K. Brown as Randall, Chrissy Metz as Kate from NBC's "This is Us."

The family’s story unfolds on screen out of chronological order – like mixed up pieces of a puzzle.

“We know the full picture of the family in the writer’s room – I know it in my brain,” creator Dan Fogelman said in a recent interview with CNN. “But as far as what the audience is going to see every week, they’re going to be getting it in bits and pieces.”

Some episodes show the children as babies, others when they’re 8 years old. One upcoming hour will show their parents in pre-kid life. The adult versions of the siblings – played by Emmy winner Sterling K. Brown, Justin Hartley, and Chrissy Metz – have appeared in every episode so far and often bring levity to the show through their spot-on delivery.

Fogelman compared the storytelling in “This is Us” to home videos played out of order.

At the end of episode 2, for example, the show revealed mom Rebecca was no longer with her children’s father. Instead, she walks into her son’s house with his father’s best friend in tow. The reason is still unclear to viewers. Is Jack dead? Are they divorced? If so, when did that happen? Answers will come, Fogelman promised.

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“You know how when you’re a kid and your teacher asks you to show your work when you’re doing a math problem?” he asked. “I think this season we’ll get a lot of answers about the facts of this family – the final answer. But we’re going to leave a lot of the showing your work to be told in the course of the season and in upcoming seasons.”

Here’s what we know so far: Kevin (Hartley) is an actor who leaves a high-profile but unsatisfying gig in search of artistic validation. Kate (Metz) is a personal assistant whose weight loss journey has stopped her from pursuing her own adventure – until a new friend and love interest comes into her life. And Randall (Brown) is a successful family man who goes searching for his birth father, William (Ron Cephas Jones), and quickly forms a connection with the former addict who once abandoned him at a fire station.

Last week’s episode delved deeper into ailing William’s story – from the moment he met Randall’s mother to the day he watched a stranger take home his son from the hospital. The series, Fogelman said, aims to use these emotional sidebars to inform the core characters.

Mandy Moore as Rebecca on NBC's "This is Us."

“Our parents aren’t just these beings who were created to birth us and came into being when we were born,” he said. “Our parents existed long before we did and had lives and loves and heartbreak and loss, and I think the reason it’s important to open up the worlds of all our characters – especially the parents – is to keep opening up this big diorama that is our lives.”

Fogelman, who also wrote 2011’s “Crazy, Stupid, Love,” never set out to create television’s most heart-tugging series – or to be a counter to a culture of cynicism. It just happened.

“The times I’ve had the most success in my career is when I’ve just sat down to write something I just wanted to write without thinking how it was going to be seen or who was going to make it,” he said.

Over the weekend, NBC entertainment president Jennifer Salke told a crowd at the Austin Film Festival that the show’s success might stem from a craving for positivity, according to The Hollywood Reporter.

“I think the current climate is so fraught with negativity and peril that people just want to enjoy something that feels smart, sophisticated, but has a warmth to it and makes them feel like they want to share it,” she reportedly said.

Brown had a similar gut feeling after his first time reading the pilot. Earlier this summer, just before he picked up an Emmy for his role in “The People v. O.J. Simpson: American Crime Story,” he told CNN that he never doubted that Fogelman’s “unique” voice would resonate – even on broadcast TV, where it’s increasingly hard to get a new show to stand out.

“I think any time – whether it’s network or cable – when a voice is able to come through in a very singular and specific way, people are drawn to it,” he said.

And if there’s any new broadcast show worth paying attention to, this is it.