LOS ANGELES (Variety.com) - Falling squarely into what has become SundanceTV's niche of spare, slow-moving, decidedly bleak dramas, "One Child" yields a devastating portrait of China's one-child policy and an adopted young English woman's unexpected desire to connect with her roots. Narratively uneven and at times exasperating in the characters' choices, this four-hour miniseries nevertheless sets up a sobering scenario, with Katie Leung (best known for the "Harry Potter" movies) as a student suddenly thrust into a life-or-death scenario, trying to navigate a Chinese system steeped in corruption. While far from perfect, the story ultimately yields a potent emotional wallop.

Raised in London by her adopted parents (Donald Sumpter, Elizabeth Perkins), Leung's Mei is contacted by a Chinese journalist (Linh-Dan Pham) who has tracked her down to deliver some shocking news: After Mei was given up, her parents had a son (Sebastian So), who has been wrongly convicted of a murder he didn't commit, with the actual killer having been spared thanks to his well-connected family.

Although Mei's initial reaction, understandably, is to wonder what possible effect she can have on the proceedings, she agrees to travel to Guangzhou, where she meets her mother (Mardy Ma, simply heartbreaking), who in their first awkward encounter can't even bring herself to look at her daughter. Yet what Mei thought was a birthmark turns out to have been a scar put there by Mom, hoping it would allow her to identify the infant if she ever returned.

With her brother sentenced to death, Mei goes about the task of trying to convince witnesses to change their perjured accounts, aided by the reporter, local activists and eventually a private detective (Junix Inocian). As for why her presence is supposed to produce results, the not-particularly-convincing thought is that a Westerner will have more latitude to challenge the authorities than Chinese citizens would.

Mei's parents are flummoxed by the whole affair, though her father rightly characterizes this as the defining moment in his daughter's life, while Mom simply worries that they'll lose her. The schemes to help, however, consistently sound almost absurdly half-baked, eventually requiring Mei to put herself at considerable risk -- and face one ethical dilemma after another.

For all that, "One Child" zeroes in on the raw emotion of the situation in a compelling way, from the mother's grief and shame to Mei's confusion to her brother's almost childlike belief that somehow his London-bred sister will be able to fix everything. And if it's a flawed exploration of the old nature-vs.-nurture debate, the players and Mei's predicament consistently make it interesting.

Heavily subtitled, the miniseries -- written by Guy Hibbert, and directed by John Alexander -- delivers a pointed commentary about the brutality of the Chinese regime. Coming on the heels of "The Honorable Woman," this latest BBC collaboration also further establishes Sundance's credentials as a channel exploring an indie film sensibility while looking to the cultural clashes that occur beyond U.S. borders in pursuit of compelling stories.

The result might not be cheery or uplifting. But in a crowded field, credit Sundance with having again found a way to leave its mark.