A sullen boy—12, at the oldest—makes an abandoned shell of a house into a home with his younger sister. With time, you gather they have nowhere else to go. Sibling actors Tucker and Savannah Sears are silent companions through much of St. Nick, their intent handyman process detailed by director David Lowery. As much as possible, Lowery dispenses with any direct reference to life outside the characters’ immediate runaway reality, aligning St. Nick with a strain of American Indie-an taciturnity in which character development is sublimated (or obfuscated) through cinematography. (St. Nick is shot on digital video by Clay Liford, and cut in off-speed combinations of scuffling handheld and austere composure.) The child performers are limited, while the filmmaking is too discrete, finally, to touch on the raw spots of childhood. What drove these kids out into the cold world—dead parents? Abuse? Foster-care mishandling?—is kept as private as the reasoning behind the title. Like a child bluffing at knowing a secret, St. Nick teases and frustrates. Set in a weedy North Texas behind No Trespassing signs, in the straggling urban-rustic ghost towns of old working-class suburbs where distant barking dogs and passing-through trains somehow make the night quieter, Lowery’s film only offers the obscure magnetism of decay as explanation.