Set during the final weeks in the life of North Korea’s late “supreme leader,” Kim Jong-il, “Commitment” underscores shifting loyalties and power-grabbing during a transition in that combative country.

The fact that “Commitment” makes the point through a gritty action story built around a tragic anti-hero and two unexpectedly sweet relationships drives home how innocent people get trapped in webs of corruption and intrigue.

First-time director Park Hong-soo brings equal amounts of delicacy and explosiveness to the engrossing tale of Myung-hoon (Choi Seung-hyun), a 19-year-old North Korean imprisoned with his sister Hye-in (Han Ye-ri) in a harsh labor camp. The two are locked away following the death of their father, a spy caught in South Korea.

Myung-hoon is offered the chance to save Hye-in from a cruel fate by agreeing to become an assassin operating in South Korea. Single-minded in his goal to protect his sister, Myung-hoon infiltrates the neighboring nation and takes an alias as a quiet student, killing targets at night.

But Myung-hoon draws unwanted attention — and feels unwanted feelings — when he demolishes bullies harassing a female student (Kim Yoo-jung). The fact that her name also happens to be Hye-in, and that she becomes a de facto second sister to Myung-hoon, brings a fablelike element to “Commitment” — the sense of an ideal above power, something worth living and fighting for.

Indeed, in this expansive, even elegant movie, Myung-hoon turns from assassin to knight-errant in pursuit of a virtue he barely has time to understand. His rapid evolution is nothing short of moving.

Tom Keogh: tomwkeogh@yahoo.com