Writer-director Joshua Marston’s drama Maria Full of Grace — about a young Colombian woman (a luminous Catalina Sandino Moreno) who attempts to break out of her impoverished life by becoming a drug mule — is riveting and heartbreaking. The same can be said of Marston’s commentary, which occasionally haunts with true-life stories of heartbreak gathered as part of his extensive research. His commentary (a must for aspiring film students) is also a compellingly in-depth account of how a wobbly-sounding drug-war polemic evolved into something more intimate and subtle. The first-time feature director was — as he repeatedly points out — immensely aided by a gifted, improvisatory cameraman and cast. But he was also artist enough to mold his footage into a taut spiral of heightened emotions that feels bracingly real.