If Pulitzer Prize–winning playwright Sam Shepard, as he says in Shepard & Dark, has “always set [himself] up as a great enemy of sentimentality,” much of the documentary—the debut film of Treva Wurmfeld—takes the opposite tack. Wurmfeld explores Shepard’s 40-year correspondence with friend Johnny Dark, but her movie doesn’t read much from those letters, which Shepard and Dark have reunited to attempt to sell them to a publisher. Instead, it more often shows the pair razzing each other in between rifling bemusedly through the leafy towers, with bright acoustic guitar ladling on the nostalgia. Wurmfeld intercuts scenes from the present with footage and photos from Dark’s meticulously kept archives from when Shepard and he lived together in the 1970s and early ’80s, with Dark married to an older woman and Shepard married to her daughter. But despite its unusual beginnings, the friendship doesn’t offer much narrative juice. That the famously peripatetic Shepard will leave the family is a foregone conclusion, and Wurmfeld does little to explain why this pair of old pals, who speak mostly in half-smiles and jokes funny more from familiarity than cleverness, should fascinate us more than others. Only a few half-finished remarks hint at the importance of Shepard and his work. At the film’s end, a sudden cruelty suggests the more meaningful drama that might have been, one of hardening and becoming aware that one is hardened, of family as a product of a particular time and set of circumstances that aren’t always recoverable, even if you have the right people.