One Child, SundanceTV's Dec. 5-6 miniseries, might not fit the category of lighthearted holiday programming. But the intense drama, which stars Harry Potter movie alum Katie Leung as an adopted young woman who's asked to make extraordinary sacrifices on behalf of a family she doesn't know, does fit right in with Sundance's growing reputation as a destination for reliably compelling storytelling.

The network of Rectify, Top of the Lake, and, most recently, Maggie Gyllenhaal's Emmy-worthy performance in the political/spy thriller miniseries The Honorable Woman follows those dramas with One Child, in which Leung's Mei, sent to an orphanage as a baby because of China's population control policy, is asked by her birth mother to return to China and help save the life of a brother she didn't even know existed.

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"It's difficult, because I haven't been through the experience of being an adoptee," Leung, who played Harry Potter's love interest, Cho Chang, tells Yahoo TV. "John Alexander, the director, suggested that I watch a documentary called Somewhere Between, which follows four Chinese girls who've been adopted in America. It's kind of their emotional journey and the decisions that they face as teenagers and the opportunity to go and see their birth mother, at that age when they're hitting puberty and all the rest. I based a lot of Mei's character on just observing these girls."

In the exclusive clip below, Mei, an astrophysics student in England, meets for the first time her sweet brother Ajun (Sebastian So), who's been framed for the murder of an African trader outside a club in his hometown of Guangzhou. Ajun has been sentenced to death — as a stand-in for the real murderer, the son of a wealthy, politically connected businessman — and his mom, Liu Ying (Mardy Ma), has reached out to birth daughter Mei for help.

"It's a very special moment [when Mei and Ajun meet], and it's one of the very few times that Mei actually gets to spend time with her brother," Leung says. "That was a really important scene, and we had to get it right. We had to capture that bond they have right away, and you can't force these things.

"Sebastian, who plays my brother, he's such a lovely person, and he has such a sweet, innocent face. The funny thing is, I didn't meet him until we had started filming. I think we just got lucky that we bonded so quickly."

Mei, immediately charmed and connected to the hopeful Ajun, doesn't click so easily with her mother who placed her at the orphanage. What ensues is an emotional, sometimes devastating trip for Mei and her birth family, touching on everything from political corruption and human rights issues to maneuvering an unfamiliar culture and an international drug and prostitution businesses.

All those issues are tackled and made relatable via Mei, a strong, caring, principled young woman who makes sacrifices big and dangerous in the interest of people she's just met, and in one of the miniseries' most heartbreaking scenes, in the interest of a stranger.

"It was a very emotional role and very difficult to prepare for," says Leung, whose role as Mei called on her to engage in activities far more adult than her innocent kiss with Daniel Radcliffe in Harry Potter and the Order of the Phoenix. The journey Mei embarks on in the two-week time period One Child spans, in fact, is as un-Potter-like as anything Radcliffe experienced while playing Beat poet Allen Ginsberg in Kill Your Darlings, as Emma Watson dropping an F-bomb in This Is the End, as Rupert Grint playing Ed Sheeran's unhinged stalker in Sheeran's "Lego House" video, and as Robert Pattinson's post-Cedric Diggory role playing a murderous billionaire in Cosmopolis.

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"Which is why, as soon as I finished production, then I was just like, 'Yeah I need to get away. I need to… it just needs to kind of escape from my mind, because it was so real," Leung continues. "It was [difficult] playing that character and making all these decisions. But I'm happy to be involved in a project that raises those questions for the audience. That's what's most important."

One Child airs on Dec. 5-6 at 9 p.m. on SundanceTV.