In director Jon Watts’ proudly spartan thriller, two schoolboys (James Freedson-Jackson, Hays Wellford) run away from small-town Colorado, only to find themselves caught up in a go-nowhere genre exercise. One conspicuous early shot has the camera glide unimpeded through a barbed-wire fence — possibly a signal to view all that follows as merely a fantasy of preteen male wish-fulfillment. Watts and co-writer Christopher D. Ford have a good sense of dumb but deliberate kid logic, which is handy when most other forms of logic need not apply. Anyway, the boys discover the titular vehicle abandoned in a field, and take it for a fateful joyride. This draws the attention of a sheriff played with gusto by Kevin Bacon, creepily mustachioed and looking as wiry as a strand of the runaways’ rationed beef jerky. A predictable game of cat-and-mouse ensues, along with the mild downer of a film forced to follow through on what might not be an entirely feature-worthy hook. Here strutting, there limping, the movie sometimes seems at odds with itself, its characters whittled into plot-serving ciphers only to be left dawdling in scenes that take too long. There is at least the glib suspense of kids naively playing around with loaded assault rifles. Shea Whigham and Camryn Manheim co-star.