We first meet abandoned mom Ray (Leo) staring disbelievingly into the empty glove compartment of a beat-up saloon as a tear dribbles down her weather-beaten cheek.
It turns out the car was the hiding place for the cash balance of a spanking new mobile home…but her gambling addicted husband got there first and is now miles away, frittering it who knows where.
Humiliatingly, she has to turn the truck delivering the prefab house away and explain to her two sons - 15-year-old Troy (Charlie McDermott) and Ricky, five, that they won't be moving after all.
Director Courtney Hunt's superchilled debut skilfully skirts cliché and formula, focussing on the marginalised characters and their grinding life in the snow-blown margins between Canada and the USA.
It's entirely believable that a desperate Ray strikes up working criminal relationship with Mohawk single mum Lila (Upham) even after she nabs her stealing her husband's car from the forecourt of a bingo parlour.
Lila, a seasoned human trafficker, persuades Ray to join her in the scam - smuggling illegal Chinese immigrants from Canada into New York State by hiding them in the boot and driving them across the frozen - but disconcertingly creaking - St Lawrence Seaway.
It all goes smoothly - or as smoothly as it can while dodging border patrols on both sides of the river and the chance of being rooked by the vicious middlemen - until Ray and Lila are persuaded to make one more drop.
Lean of plot and rich in characterisation, this never goes for the easy option and provides a strangely satisfying ending, determinedly free of sentimentality, yet packing a powerful emotional punch.
Cold yet never calculating, it's a fine film featuring a heart-rendingly knockout performance of steel and strength from Leo.
Go with the flow.