The actors hit notes of truth in a film that seems to be about fly-fishing-as-therapy but cuts deeper.

Combat veterans, famously, don’t tend to talk much, if at all, about their experiences of war. At least not to civilians, and maybe not even to their closest relatives. Knowing this, those of us who aren’t veterans tend to have ideas about the things they aren’t discussing. Things like violence and fear and the chaos and insanity of battle. That’s surely a part of it, but in a way it’s also the heightened cinematic version, the one we’ve all gotten from war movies. What it leaves out are the torn-up emotions of soldiers, the lifelong imprint left upon them not just by the cataclysm of war but by their relationship with their fellow soldiers — the loyalty and love, the complex code of liberation and guilt at having survived.

“Mending the Line” is a drama about two veterans and their relationship to the combat experience, and the movie, which is also about fly fishing (in that metaphysical Zen-of-the-outdoors way), has a deceptively placid surface and a turbulent undertow that catches up to you. The central characters are both Marines, scarred and defined by the combat they’ve been in. When we first see John Colter (Sinqua Walls), he’s leading his platoon on their final day of deployment in Afghanistan — but, of course, that “routine” day of recon doesn’t go well. It’s an ambush from hell.