A kind-hearted drama whose consistent quiet and composure leaves you all the more floored by its conclusion, Leave No Trace takes its title from the environmentally friendly ethos for America’s parks and just how infinitesimal our nation’s grid feels for those forced to its farthest corners.

Will (Ben Foster) is an Armed Forces veteran whose rumpled keffiyeh scarf offers the sole expository key to his Middle East theatre of war. We don’t know exactly how long he and his teenaged daughter, Tom (Thomasin McKenzie), have imperceptibly — but illegally — lived on public lands. But it’s long enough that they have internalized these lushly photographed, green forests as home — with the pinch-and-dash approximations expected from a life of scarcity.

Will’s intractable idiosyncrasies spring from a not-entirely-unreasonable skepticism of the systems in place for veterans like him and their loved ones. In brief visits to their local Department of Veterans Affairs, the sole resources seem to be stress coins, coils to clog guns with which soldiers may end their lives and prescription pills Will fences to buy food and supplies. His anxieties feel classified, codified and cataloged into a system that absolutely will move on without you should you not input your answer by the timed beep. But Will’s anger is also rooted in fear, shame and a sense that he must protect Tom not from the world’s evils but from even the opportunity to make the sort of bad decisions that continue to haunt him.

Shutting Tom off from society nearly altogether has been his response. But Will can’t isolate Tom from the natural moment at which children either choose to alienate themselves from, or align with, their parents’ way of life as it’s been presented. When they are spotted and swept into bureaucratic processes by those whose mission is to resettle the unsettled, Will and Tom must wrestle with whether living among everyone else constitutes adaptation or acquiescence.

To reveal what happens to Will and Tom — beyond confirmation that re-entering into the social contract is easier said than done — would betray no major narrative revelations. But it would rob power from a complex father-daughter sketch drawn by co-writer / director Debra Granik. Here, Granik sheds even modest thriller trappings of her breakthrough film, 2010’s Winter’s Bone, for an exercise in pure, ecumenical empathy.

One character says some people wish they could live like Will and Tom, an idea perhaps justifiably chided as a first-world problem. However, Granik and co-writer Anne Rosellini (adapting from Peter Rock’s novel My Abandonment) neither dismiss that daydream nor overly romanticize Will and Tom’s choices. It understands that individuals and institutions are increasingly under assault for any number of reasons and wonders how that strain might feel.

At no point does Leave No Trace turn any character’s passions or preferences into a punchline. Neither does it erupt into violence, which may seem especially surprising for those familiar with Foster’s traditionally hotheaded work. Safe to say you’ve never seen Foster embrace such quiet or subtlety as Will tries keeping appearances of normalcy, honesty and patience amid a mental hell into which he’s huddled. McKinzie matches him beat for beat as a young woman at an age where peer judgment is at its peak and she’s disadvantaged for never having peers yet.

“How much does it matter to you, what people think of us?” Will asks. “I guess we’ll find out,” Tom replies, as much in fear as defiance. It’s the closest Leave No Trace comes to raising its voice and yet reflective of the ways in which rifts rise between those who still respect one another. Foster and McKenzie are so harmoniously in sync that there are points where McKenzie almost subconsciously seems to speak in Foster’s own tone and inflection. Each delivers a remarkable performance ranking among the year’s very best so far — Foster’s most surprising yet and, if we’re lucky, the first of many more to come for McKenzie.

Beyond this central relationship, Leave No Trace understands the obstacles to establishing a beneficial presence in bureaucracies where BS tends to be the MO or even just being the bigger person. As Jean, a caseworker assisting Will and Tom, Dana Millican excellently conveys the weary, bleary effects from riding the line of policy and common sense. At one point, a potential benefactor mentions seeing Will and Tom’s story on the news. Jean cuts him off not out of annoyance or aggression, but to keep Will and Tom from feeling either like a charity case or a curiosity to be regarded with wonder. David M. Pittman also rings true as Blane, a medic Will meets who, with a handful of lines, comes to understand Will’s psyche in endearing ways.

These are among the moments of everyday ephemera in which Leave No Trace sparks deep compassion, riveting confrontation and, eventually, truth in its characters’ compromises and consequences. Granik lets Foster and McKenzie wring simultaneous resignation and resentment from a pivotal third-act scene, but neither do any of them forget to summon humanity and dignity. One of 2018’s very best films, Leave No Trace leaves your heart cracked but not broken, and somehow still fills with warmth and tenderness that piece it leaves behind.